-NRLF 


EbE    SOh 


THE    EARTH 
IN  PAST  AGES 


VESUVIUS  IN  ERUPTION,  1872. 


STORIES  of  the  UNIVERSE 

The  Earth 

In  Past  Ages 

By 

H.  G.   SEELEY,   F.R.S. 

PROFESSOR   OF  GEOGRAPHY  AND   LECTURER   ON   GEOLOGY  AND 
MINERALOGY   IN   KING'S   COLLEGE,    LONDON 


I 

WITH  FORTY  ILLUSTRATIONS 


NEW    YORK 

REVIEW  of  REVIEWS  COMPANY 
1910 


COPYRIGHT,  1895,  1902, 
BY  D.  APPLETON  AND  COMPANY. 


PREFACE. 


I  HAVE  endeavoured  to  tell  the  story  of  the 
Earth  so  that  its  past  history  helps  to  explain  its 
present  condition. 

Explanations  are  given  of  the  nature  of  the 
common  materials  which  form  rocks,  of  the  ways 
in  which  they  rest  upon  each  other,  and  of  the 
means  by  which  they  may  be  distinguished. 

The  story  of  the  Earth  is  divided  into  epochs 
by  layers  of  rock  which  rest  on  each  other  and 
rise  to  the  surface  of  the  visible  land,  and  to  the 
floor  of  the  ocean. 

Geological  time  cannot  be  defined  in  years. 
The  time  occupied  by  an  existing  river  like  the 
Rhine  or  the  Niagara  river,  in  excavating  the 
gorge  through  which  it  flows,  dates  back  beyond 
the  antiquity  imagined  for  man  by  historians. 
Yet  this  incident  in  sculpture  of  the  Earth's  sur- 
face is  subsequent  to  the  newest  of  the  regular 
layers  of  rock.  It  is  convenient  to  forget  the 
human  standard  of  time,  and  think  of  a  period  of 
geological  time  as  the  age  when  some  rock,  such 
as  coal,  accumulated,  or  when  an  extinct  plant  or 
animal  was  dominant  on  the, Earth.  • 

Fossils  are  the  remains  of  plants  and  animals 
by  which  each  period  of  by-gone  time  is  distin- 
guished. 

5 


6  PREFACE. 

I.  Many    kinds   of   animals,   which    still    live> 
date  back  to  the  beginning  of  the  Earth's  story> 
or  to  an  early  period. 

II.  Many  groups  of  animals,   such  as  Trilo- 
bites  or  Ichthyosaurs,  endured  on  the  Earth  for 
long  geological  ages,  varied  in  form  and  struc- 
ture, and  became  extinct  successively,  leaving  no 
survivor. 

The  life  which  now  exists  on  the  Earth  is  a 
survival  of  ancient  types  of  life  known  from 
fossils,  which  have  undergone  substantially  no 
change  since  first  they  became  known  in  the 
rocks.  They  are  associated  now  with  groups, 
like  the  Mammalia,  which  are  changing  rapidly. 
The  diversity  of  mammal  orders  in  structure  of 
the  skeleton,  is  not  unlike  that  which  the  ancient 
Saurians  put  on  before  they  became  extinct. 
Animals'  orders  which  vary  rapidly  last  for  a 
relatively  short  time. 

I  have  used  some  scientific  names  of  these 
fossils  in  the  story  of  the  Earth,  since  names 
give  the  easiest  identification  for  fossils  as  for 
our  fellow-men.  The  characteristics  or  lives  of 
fossil  animals  and  of  living  men  give  interest 
to  their  names.  Practical  knowledge  of  fossils 
ensures  this  enduring  interest,  and  is  gained  by 
collecting  them  in  the  sea-cliff,  quarry,  or  pit, 
and  by  comparing  such  specimens  with  named 
examples  in  museums. 

H.  G.  SEELEY. 
KENSINGTON,  W.,  1895. 


CONTENTS. 


I.  INTRODUCTION  .       . .      .-    ,'••-.'      •  .-.••  •       .       9 
II.  THE  EARTH'S  INTERNAL  HEAT      ...      12 

III.  MATERIALS  OF  MOUNTAIN  CHAINS      v,,;  ;    .      18 

IV.  VOLCANIC  ROCKS      .        .     );  Y       .        .        .      26 
V.  THE  MATERIALS  OF  STRATA  .        •'.",»        .      31 

VI.  THE  SUCCESSION  OF  STRATA  .        .  ,-•    •        .      51 
VII.  ORIGIN  OF  STRATIGRAPHICAL  GEOLOGY         .      58 
VIII.  FOSSILS      .      T.       •;  •      .<      .      '  ..'       .        .      62 
IX.  THE     CLASSIFICATION     OF    WATER-FORMED 

ROCKS  .       .        .       .....        .        .      74 

X.  THE  ARCH^AN  ROCKS    .        .        .        .        .78 

XI.  CAMBRIAN  AND  ORDOVICIAN  ROCKS        .        .      81 

XII.  OLD  RED  SANDSTONE  AND  DEVONIAN  .        .      92 

XIII.  CARBONIFEROUS  STRATA  .        .        .        .        .97 

XIV.  PERMIAN  AND  TRIAS 115 

XV.  LIAS  .        .        .   '  ;V       .        .        .        /      .    125 
XVI.  OOLITES     .        .        .        .        .        .        .        .130 

XVII.  THE  NEOCOMIAN  PERIOD        .        .        .        .    142 

XVIII.  LOWER  CRETACEOUS  ROCKS    ....    149 

XIX.  THE  CHALK 156 

XX.  THE  LOWER  TERTIARY  STRATA     .        .        .    162 
XXI.  THE  MIDDLE  TERTIARY  PERIOD    .        .        .     173 

XXII.  THE  CRAG     ;  v  / 178 

XXIII.  GLACIAL  PERIOD  AND  GRAVELS      .        .        .182 


LIST  OF  ILLUSTRATIONS. 


VIGURB 

Vesuvius  in  Eruption,  1872        •       «       Frontispiec* 

1.  Gneiss 89 

2,  3.  Hertfordshire  Pudding  Stone        •        •        •        •  35 

4.  Laminated  Sand 39 

5.  Ripple-marked  Sandstone          •        .        •        •        .  41 

6.  Lithographic  Stone    .......  46 

7.  Carboniferous  Limestone 47 

8.  The  Chalk  in  Yorkshire 56 

9.  Snowdon  to  Flintshire       ••••••  83 

10.  Inlier  at  Usk     ....        .        • '      .        .87 

11.  Feet  of  the  Trilobite.        ......  91 

12.  To  the  Forest  of  Dean      ......  93 

13.  East  of  the  Pennine  Chain loo 

14.  Productus  .        .        .        .        .        .        .        .        •  IOI 

15.  Pleu rot om aria IO2 

16.  Sigillaria    .        \ Iio 

17.  Teniseopteris     •••.....  Hi 

18.  Pareiasaurus 119 

19.  Lias  Outlier 126 

20.  Gryphsea  Incurva       .        •        •        •        •        •        ,127 

21.  Cardinia  Listen 128 

22.  Ichthyosaurus    .....*..  131 

23.  Belemnites  Oweni 136 

24.  Shotover  Hill 137 

25.  Skeleton  of  Archseopteryx         .        .        .        .        .139 

26.  Skull  of  Archseopteryx 140 

27.  Hythe  to  Folkestone 148 

28.  Ammonites  Deshayesii       .         .        .         .        .         .150 

29.  Section  at  Hunstanton       .        .        •        •        •        •  I5I 

30.  Ammonites  Planulatus       .         •         •         •         •         .152 

31.  Poterocrinus       ........  153 

32.  Micraster  Coranguinum 159 

33.  Galerites  Subrotundus 160 

34.  East  of  Herne  Bay 164 

35.  Ostrsea  Bellovacina 165 

36.  Cyprina  Morrisi 166 

37.  Strata  in  Alum  Bay  .......  169 

38.  Planorbis  Euomphalus       .         .         •'*''•         •  175 

39.  Cardita  Senilis  ........  179 

40.  Fusus  Antiquus  reversed  ......  181 


THE  STORY  OF  THE  EARTH. 


CHAPTER  I. 

INTRODUCTION. 
I. 

THE  building  of  the  surface  layers  of  the  Earth 
is  recorded  in  rock  materials,  which  are  accumu- 
lated upon  each  other.  But  there  is  no  trace  of  a 
beginning  to  their  story  of  the  Earth's  history. 
In  the  remotest  period  of  past  geological  time  of 
which  evidence  has  been  found,  the  earth  was  in- 
habited by  types  of  animals,  some  of  which  still 
survive.  There  is  no  evidence  that  the  most 
ancient  animals  which  have,  been  discovered  were 
the  first  that  existed,  or  that  the  oldest  rocks  at 
present  known  mark  the  beginning  of  geological 
records.  It  is  as  unprofitable  to  enquire  for  evi- 
dences of  the  origin  of  the  earth,  as  it  is  to  ask 
for  proofs  of  the  mode  of  origin  of  the  life  which 
has  flourished  upon  it. 

Because  the  earth  is  a  planet  we  may  assume 
that  it  had  a  similar  history  in  its  origin  to  some 
of  the  heavenly  bodies.  The  light  which  comes 
to  the  earth  from  the  most  distant  stars  in  the 
universe,  proves,  when  analysed,  to  result  from 
the  incandescence  of  elements  which  are  mostly 
identical  with  those  found  in  the  earth.  The 
small  masses  of  matter,  termed  meteorites,  which 
fall  from  time  to  time  to  the  earth's  surface,  con- 


10  THE   STORY  OF  THE   EARTH. 

sist  of  iron  and  other  metals,  and  of  minerals  like 
those  which  combine  to  form  crystalline  rocks. 
The  forces  which  act  on  the  earth  are  like  those 
manifested  in  other  heavenly  bodies.  If  the 
Earth's  surface  is  not  incandescent,  as  in  the 
luminous  stars,  its  interior  demonstrates  in  many 
ways  an  internal  heat,  which  has  played  an  im- 
portant part  in  its  history.  So  that,  with  the  mat- 
ter and  force  substantially  the  same,  there  is  some 
justification  for  the  old  definition  of  geology  as 
that  department  of  astronomy  which  tells  the 
story  of  the  Earth. 

The  geological  story  differs  from  that  told  by 
the  astronomer  in  giving  results  of  unceasing  ac- 
tion of  the  forces  of  nature  upon  the  rock  materi- 
als of  the  globe.  They  have  worked  during  a  time 
which  is  immeasurably  long,  when  estimated  by 
such  changes  on  the  earth  as  have  happened  dur- 
ing human  history.  This  time  cannot  be  expressed 
in  centuries.  The  work  of  rivers  in  carving  chan- 
nels upon  the  existing  surface  of  the  earth  has 
been  computed  at  from  15,000  to  30,000  years,  in 
the  case  of  Niagara  river,  without  reaching  the 
age  when  the  newer  layers  of  the  globe  were  de- 
posited from  the  sea.  This  stupendous  duration 
of  time  has  brought  about  revolutions  in  the  po- 
sitions of  oceans  and  continents  ;  in  the  types  of 
life  which  were  predominant  on  the  earth,  as  well 
as  in  the  distribution  of  life  over  the  globe,  and 
in  the  succession  of  different  kinds  of  life  in  the 
same  region  in  successive  ages,  which  would  be 
incredible  but  for  the  evidence  of  fossil  animals 
and  existing  animals  which  are  everywhere  around 
us.  These  changes  have  come  about,  not  as  result 
of  catastrophes  which  have  destroyed  the  fair  sur- 
face of  the  land  and  its  life,  but  as  parts  of  the 


INTRODUCTION.  1 1 

order  of  nature,  and  as  conditions  of  that  stability 
of  government  of  the  world  by  which  the  cre- 
ations of  earlier  times  have  been  preserved,  and 
passed  on  from  one  geological  age  to  another  to 
survive  at  the  present  day. 


ii. 

On  various  parts  of  the  globe,  meteorites  have 
been  found  which  vary  in  weight  from  a  few  ounces 
to  a  few  tons.  Examples  of  400  of  them  are  pre- 
served in  the  British  Museum.  Some  have  been 
seen  to  fall.  It  may  therefore  be  inferred  that 
ever  since  the  earth  has  been  in  existence  it  has 
probably  received  such  additions  of  material. 
Meteorites  however  do  not  demonstrate  that  the 
earth  has  been  built  up  of  meteoric  matter;  but 
they  are  the  only  clue  of  a  practical  kind  to  the 
origin  of  the  globe,  which  the  geologist  encoun- 
ters. 

The  iron  in  meteorites  is  metallic,  usually  com- 
bined with  nickel.  In  the  earth  iron  is  rarely  me- 
tallic, and  rarely  crystallized  with  nickel.  Minute 
particles  of  metallic  iron  are  present  in  the  vol- 
canic rock  named  Basalt,  which  has  flowed  over 
the  north  of  Ireland.  Iron  is  found  combined 
with  nickel  in  the  Van  mine  in  Denbighshire. 
The  percentage  of  nickel  in  the  iron  varies  in 
different  localities.  There  is  only  one  or  two  per 
cent,  of  nickel  in  the  great  masses  of  iron,  some- 
times weighing  50,000  Ibs.,  embedded  in  Basalt  at 
Ovifak  in  Disco  Island,  on  the  west  of  Greenland. 
An  alloy  of  these  metals  found  in  New  Zealand, 
yields  67  per  cent,  of  nickel.  Both  are  regarded 
as  of  terrestrial  origin. 

Although  the  mineral  quartz  is  one  of  the  most 


12  THE   STORY  OF  THE  EARTH. 

abundant  constituents  of  surface  rocks,  no  true 
quartz  has  been  recognised  in  any  meteorite.  But 
a  rare  mineral  asmanite  with  many  of  the  proper- 
ties of  quartz  occurs,  which  somewhat  resembles 
the  variety  of  quartz  found  in  some  volcanic 
rocks,  which  has  been  distinguished  under  the 
name  tridymite. 

About  ten  rare  minerals  are  met  with  in  me- 
teorites which  have  never  been  recognised  in  the 
rock  materials  of  the  globe. 

On  the  other  hand,  earthy  meteorites  have 
yielded  many  of  the  constituents  of  volcanic  and 
crystalline  rocks. 

Two  kinds  of  felspar — named  labradorite  and 
anorthite — have  been  recorded  in  meteorites,  and 
such  minerals  as  Augite,  Bronzite,  Enstatite,  Oli- 
vine,  which  upon  the  earth  are  often  combined  with 
the  felspars  in  mineral  union  to  form  crystalline 
rocks.  But  the  facts  are  too  few  and  too  obscure 
to  do  more  than  stimulate  interest  in  the  relation 
of  the  earth  to  the  bodies  among  which  it  moves. 


CHAPTER  II. 
THE  EARTH'S  INTERNAL  HEAT. 

THE  earth  has  an  internal  heat  of  its  own, 
which  is  not  derived  from  the  sun.  The  temper- 
ature of  the  outer  surface  layer  varies  with  sum- 
mer and  winter.  In  Java  and  India  at  a  depth  of 
12  feet  the  thermometer  is  constant  all  the  year 
round.  In  London  and  Paris  an  unvarying  tem- 
perature occurs  at  about  100  feet  below  the  earth's 
surface.  The  earth's  heat  begins  to  increase  be- 


THE  EARTH'S   INTERNAL  HEAT.  13 

low  this  variable  surface  layer,  though  the  rate  of 
increase  differs  with  the  kinds  of  rock  passed 
through,  and  with  the  locality.  It  averages  one 
degree  Fahrenheit  for  every  55  feet  of  depth. 

In  the  famous  Artesian  well  at  Grenelle  near 
Paris,  the  water  rose  from  a  depth  of  1794  English 
feet,  with  a  temperature  of  nearly  82°  F.  The 
deep  boring  at  Sperenberg  near  Berlin  appears  to 
show  an  increase  of  i°  F.  in  42  feet  at  the  depth 
of  TOCO  feet;  i°  F.  in  57  feet,  at  2000  feet;  and  i° 
F.  in  95  feet,  at  3000  and  4000  feet.  From  these 
facts  the  inference  has  been  made  that  tempera- 
ture does  not  augment  appreciably  below  a  mod- 
erate external  thickness  of  rock. 

The  difference  between  the  surface  tempera- 
ture and  the  interior  temperature,  results  from  the 
loss  of  the  earth's  internal  heat  by  radiation.  On 
this  circumstance  attempts  have  been  made  to  es- 
timate the  duration  of  geological  time.  By  meas- 
uring the  amount  of  heat  which  the  earth  radiates 
from  its  surface  in  a  year,  Lord  Kelvin  has  con- 
cluded that  in  a  period  of  20,000  millions  of  years, 
more  than  enough  heat  would  have  been  lost  to 
melt  the  entire  bulk  of  the  earth,  if  the*  rate  of 
loss  had  been  always  what  it  is  now,  and  if  the 
earth  had  consisted  throughout  of  the  same  ma- 
terials as  its  surface  rocks.  This  is  the  time  which 
the  physicist  conceives  as  possible  for  the  earth's 
origin  and  history.  Sir  John  Herschel  had  doubt- 
ed the  primitive  fluidity  of  the  earth.  It  is  per- 
haps possible  that  the  heat  which  the  earth  loses 
may  not  be  the  original  heat  of  an  igneous  fusion, 
but  the  result  of  strain  due  to  its  rigid  state.  It 
rotates  so  that  its  surface  experiences  the  lifting 
influence  of  tidal  attraction  which  reduces  the 
pressure,  although  the  amount  is  too  small  to  dis- 


14  THE   STORY   OF   THE   EARTH. 

1  % 

turb  the  stability  of  its  surface.  By  the  conver- 
sion of  this  attraction  of  gravitation  upon  its 
outer  layers  into  heat,  at  a  depth  from  the  surface 
sufficient  to  ensure  that  the  heat  so  generated 
could  not  be  radiated  in  a  day,  a  store  of  heat 
might  accumulate  near  to  the  surface  of  the  globe. 
The  most  ancient  rocks  give  no  evidence  of  greater 
internal  heat,  or  of  greater  refrigeration  of  the 
earth,  or  of  tidal  action  upon  its  surface  having 
been  in  any  way  different  from  what  it  is  now. 

The  greatest  depth  at  which  the  fractures  and 
dislocations,  termed  earthquakes,  are  known  by 
actual  measurement  to  originate,  is  about  30 
miles.  It  has  also  been  calculated  that  a  heat 
sufficient  to  melt  granite  might  occur  at  a  depth 
of  20  or  30  miles.  This  is  the  maximum  depth  to 
which  geological  theory  extends  its  inferences. 

Attempts  have  been  made  to  calculate  the 
pressure  under  which  masses  of  granite  in  moun- 
tain chains  have  consolidated.  In  some  cases  the 
crystal  structure  appears  to  indicate  a  superin- 
cumbent pressure  equal  to  no  more  than  15  miles' 
thickness  of  rock,  though  the  pressure  was  proba- 
bly lateral. 

The  materials  ejected  from  volcanos  give  no 
indication  of  having  ascended  from  more  than 
very  moderate  depths.  The  molten  matter  of 
lava  streams  does  not  appear  to  be  the  primitive 
substance  of  the  earth's  interior.  That  heated 
material  might  be  rendered  liquid  by  fractures 
which  penetrate  downward  so  as  to  remove  the 
pressure  which  keeps  the  heated  rock  solid.  It  is 
thus  manifest  that  some  cause  generates  heat  near 
to  the  earth's  surface,  which  is  associated  with  the 
crumpling  of  the  earth's  outer  layers,  with  the 
changed  distribution  of  level  of  land  from  age  to 


THE  EARTH'S  INTERNAL  HEAT.        15 

age,  and  with  the  phenomena  of  volcanic  ac- 
tivity. 

This  cause  is  believed  to  be  the  cooling  of  the 
earth ;  by  which  the  shrinkage  of  the  deeper  lay- 
ers crushes  the  upper  layers  together,  crumpling 
them  into  folds  which  are  directed  alternately  up- 
ward and  downward.  As  these  folds  are  crushed 
closer  together,  the  mechanical  energy  of  com- 
pression, resisted  by  the  rock  material,  becomes 
converted  into  heat  along  the  lines  of  most  intense 
squeezing;. 

The  directions  of  these  folds  change  from  age 
to  age  in  geological  time;  for  every  land  consists 
of  masses  of  rock  which  extend  through  it  in  direc- 
tions which  were  once  approximately  parallel  to 
its  shores. 

The  late  Mr.  Robert  Mallet  believed  that  the 
energy  of  volcanic  eruptions  was  developed  by 
these  compressions  of  the  crust.  He  also  urged 
that  the  lateral  pressure  exerted  by  the  sides  of 
an  arch  of  continental  land  upon  its  supports 
would  result  in  crushing  along  the  lines  of  greatest 
weakness;  and  calculated  that  the  temperature 
may  be  raised  locally  in  this  way  to  a  red  heat,  or 
even  to  the  fusing  point  of  the.  rocky  ^materials 
which  are  crushed.  This  heat,  which  is  produced 
locally,  he  believed  to  be  consumed  locally,  and  to 
be  the  source  of  the  explosive  energy  which  ejects 
the  materials  of  which  volcanos  are  built  up. 

Active  volcanos  are  commonly  met  with  in 
regions  undergoing  upheaval.  This  is  attributed 
to  the  underground  compression  of  the  rocks 
which  causes  upheaval,  generating  heat.  The 
water  near  the  shore  which  penetrates  to  the 
heated  region  is  raised  by  that  heat  to  an  explo- 
sive temperature.  Volcanos  have  a  linear  exten- 


1 6  THE  STORY  OF  THE  EARTH. 

sion ;  sometimes  in  islands  rising  from  the  sea, 
sometimes  in  mountain  chains  formed  of  islands 
united  together.  The  linear  arrangement  is  at- 
tributed to  the  opening  of  fissures,  which  pen- 
etrate downward  along  lines,  in  which  the  rocks 
have  been  folded  and  fractured  in  the  process  of 
upheaval.  When  rain  water,  in  a  region  so  bent 
and  strained,  is  held  back  upon  the  land  and 
hindered  from  escaping  by  the  pressure  of  the  sea 
round  its  shores,  the  water  descends  through  the 
minor  joints  and  capillary  interspaces  between  the 
particles  of  rock.  Then  it  rises  in  temperature 
with  the  internal  heat  of  the  earth,  so  as  to  facil- 
itate the  melting  of  rocks,  with  which  it  combines. 
Some  of  this  water  eventually  ascends  through 
the  planes  of  fracture  and  displacement  forming 
outlets  for  explosive  energy,  discharging  steam, 
dust,  and  the  rock  matter,  both  solid  and  molten, 
which  builds  volcanic  cones. 

The  past  periods  of  geological  time  abound  in 
evidences  of  volcanic  activity.  From  the  imper- 
fect nature  of  the  records  which  remain  upon  the 
earth  their  linear  arrangement  is  not  always  evi- 
dent ;  but  they  may  be  inferred  to  mark  lines  of 
upheaval  which  brought  islands  into  existence,  or 
united  them  into  continental  masses  of  land  in 
successive  epochs  of  geological  time.  But  be- 
sides the  volcanos  which  are  marked  by  beds  of 
ashes  and  lava-flows,  and  the  throats  up  which 
the  molten  matter  ascended,  there  are  in  many 
parts  of  the  world  extinct  volcanos  with  their 
cones  well  preserved,  as  though  the  craters  had 
been  recently  active. 

A  little  south  of  the  Pyrenees,  in  the  basin  of 
the  Ebro,  there  are  fifteen  cones  about  Olot  in 
Catalonia,  built  of  cinders,  from  each  of  which 


THE  EARTH'S  INTERNAL   HEAT.  17 

lava  has  flowed  in  streams  still  to  be  traced,  yet 
so  long  since  that  the  existing  rivers  have  cut 
passages  for  themselves  through  the  lava. 

The  Auvergne  is  a  granite  platform  in  which 
some  ancient  rocks  of  the  carboniferous  period 
occur.  This  district  appears  to  have  been  an  is- 
land traversed  by  a  line  of  fracture  from  N.W.  to 
S.E.,  which  corresponds  to  the  uplifting  of  the 
crystalline  rocks.  A  second  fracture  runs  from 
N.  to  S.  In  this  region  are  the  ruins  of  the  four 
grand  volcanos  known  as  Mont  Dore,  Cantal, 
Canton  d'Aubrac,  and  Mezen.  The  lava  flowed 
from  Mont  Dore  for  20  miles.  The  minor  cones, 
of  which  there  are  hundreds,  range  through  the 
country  in  a  broad  band,  from  N.  to  S.  Many 
have  the  craters  burst  down  by  the  lava  which 
ascended  in  them,  and  overflowed  into  the  neigh- 
bouring valleys. 

Beautifully  preserved  volcanic  cones  are  found 
to  the  north  of  the  Moselle  river  in  the  district 
known  as  the  lower  Eifel.  It  may  have  been  in 
this  country  that  the  eruption  took  place  which  is 
mentioned  by  Tacitus  as  having  affected  the 
country  near  Cologne,  in  the  reign  of  the  Roman 
Emperor  Nero.  For  a  long  way  up  tho  Rhine 
the  rocks  are  volcanic ;  and  evidences  of  extinct 
volcanos  are  found  west  of  the  Rhine,  in  many 
parts  of  central  Germany;  and  a  series  ranges 
through  Hungary  S.W.  of  the  Carpathians  into 
Servia. 

The  latest  volcanic  outbursts  in  the  British 
Isles  were  at  the  beginning  of  the  Tertiary  period 
in  Skye,  Rum,  Mull  and  the  adjacent  mainland  of 
Scotland,  and  in  the  north  of  Ireland,  where 
streams  of  mud  due  to  volcanic  dust,  washed 
down  by  rains,  covered  up  the  vegetation  of  the 


1 8  THE   STORY   OF   THE   EARTH. 

country  before  it  was  deluged  with  the  black  lava 
named  basalt.  Branches  of  the  conifer  Sequoia, 
and  of  plane  trees  covered  with  leaves,  are  pre- 
served in  the  consolidated  mud  which  underlies 
these  lava-flows. 


CHAPTER   III. 

THE    MATERIALS    OF    MOUNTAIN    CHAINS. 

THE  same  cause  which  produced  the  local  heat 
and  fractures  which  led  to  volcanic  outbursts,  has 
folded  the  earth's  crust.  Rocks  many  thousands 
of  feet  thick  have  been  bent,  folded  and  crumpled. 
This  structure,  which  is  shown  in  the  succession 
of  rocks  on  the  surface  of  every  country,  in  folds 
termed  saddles  and  troughs,  is  most  astounding  in 
its  intensity  in  mountain  chains.  The  upheaving 
of  the  parallel  ridges  of  limestone  rock  known  as 
the  Jura  chain,  forming  the  frontier  between 
Switzerland  and  France,  is  a  beautiful  example  of 
troughs  which  form  valleys,  parting  the  elevated 
ridges  from  each  other.  In  that  part  of  the  Alps 
known  as  the  Grisons,  all  the  geological  deposits, 
from  the  tertiary  down  to  the  oldest,  have  been 
turned  upside  down,  in  the  process  of  folding  by 
lateral  displacement ;  which  is  the  sole  cause 
which  lifts  mountain  ranges.  The  curved  form  of 
the  earth  necessitates  that  every  axis  of  elevation 
must  be  accompanied  by  spurs  at  right  angles  to 
itself,  or  by  parallel  ranges.  The  parallel  system 
is  exemplified  in  the  chains  of  North  America, 
which  lie  between  the  Rocky  Mountains  and  the 
Pacific. 


THE   MATERIALS   OF   MOUNTAIN   CHAINS.       19 

These  folds  once  formed  remain  for  all  time. 
They  may  be  raised  higher,  or  depressed  beneath 
the  sea,  and  new  rocks  laid  down  upon  them ; 
but  as  those  ancient  folds  increase  in  intensity 
with  the  slow  succession  of  geological  ages,  the 
newer  rocks  become  folded  with  their  folds,  and 
the  folds  run  in  the  same  direction. 

In  such  puckered  and  crumpled  rocks  as  moun- 
tain chains  exhibit  on  their  denuded  heights,  there 
is  almost  invariably  evidence  of  a  crystalline  tex- 
ture. This  may  be  attributed  to  the  influence  of 
the  heat  produced  by  the  mechanical  power,  trans- 
formed by  the  resistance  which  the  rock  mass  of- 
fered to  compression. 

The  rocks  which  form  mountains  are  chiefly 
slaty  rocks,  and  schists,  with  here  and  there  some 
granite  masses  or  sheets  of  volcanic  rock.  They 
have  only  been  laid  bare  by  the  removal  of  vast 
thicknesses  of  water-formed  rock  which  once  ex- 
tended above  them.  If  the  crystalline  materials 
are  not  the  necessary  products  of  the  upward 
thrust  of  the  mountain  chain  and  adjacent  land 
which  supports  it,  it  may  be  difficult  to  account 
for  the  uniform  character  of  the  rocks  of  which 
the  durable  central  masses  of  mountain  cnains  are 
built.  There  are  stages  in  this  process  of  change. 
The  flanks  of  a  mountain  range  commonly  show 
the  fine  microscopic  crystalline  texture  of  slate, 
while  the  central  masses  show  the  coarse  crystal- 
line texture  of  schist,  or  granite. 

Slate. — The  part  which  slate  plays  in  the  forma- 
tion of  mountain  masses  is  well  seen  in  the  struc- 
ture of  the  mountainous  regions  of  North  and 
Central  Wales,  in  parts  of  the  Lake  District  in 
Westmoreland  and  Cumberland,  and  in  the  south 
of  Scotland.  It  is  certain  that  slate  was  originally 


20  THE   STORY   OF   THE   EARTH. 

a  water-formed  rock,  a  mud  which  consolidated 
into  clay.  It  often  shows  successive  parallel  beds 
marked  by  differences  of  colour.  Welsh  slates 
sometimes  contain  clay  pebbles,  such  as  occur  at 
the  present  day  on  shores  where  the  cliffs  are  of 
compact  clay.  Many  slates  contain  fossil  remains 
of  animals  which  lived  in  the  sea  when  the  old 
mud  was  accumulating.  Those  fossils  are  often 
distorted  and  squeezed  into  half  their  original 
breadth  or  length,  showing  that  the  whole  moun- 
tain mass  has  undergone  compression  and  con- 
densation. The  compression  has  bent  the  rocks 
into  synclinal  troughs  and  anticlinal  saddles. 
The  slaty  texture  is  most  developed  in  the  troughs. 
The  effect  of  this  lateral  pressure  has  been  in 
the  first  place  to  turn  the  films  of  water  contained 
between  the  particles  of  the  old  mud  at  right 
angles  to  the  direction  from  which  the  pressure 
came.  The  resistance  offered  by  the  rock  trans- 
formed a  large  part  of  the  motion  imparted  to  its 
particles  into  heat.  That  heat  raised  the  temper- 
ature of  the  water  contained  in  the  rock,  enabling 
each  film,  under  the  pressure,  to  dissolve  some 
constituents  of  the  mineral  matter  in  which  it  was 
contained.  These  slaty  rocks  often  give  evidence 
of  having  been  fractured  through  their  thickness 
by  minute  dislocations,  and  subsequently  re-united. 
Such  breakage,  relieving  the  pressure,  would  cause 
the  temperature  to  fall,  and  the  substances  which 
had  been  dissolved  then  crystallize  in  minute 
films,  parallel  to  each  other,  extending  throughout 
the  mountain  mass,  and  having  no  relation  to  the 
original  planes  in  which  the  mud  was  deposited. 
These  microscopic  crystal  films  resemble  such  min- 
erals as  mica  or  chlorite.  They  impart  to  the 
rock  the  property  termed  slaty  cleavage.  This 


THE  MATERIALS   OF   MOUNTAIN   CHAINS.       21 

cleavage  causes  it  to  split  in  layers  which  cut 
across  the  original  folded  or  faulted  planes  of 
bedding.  This  microscopic  crystalline  change  of 
texture  imparts  to  the  rock,  now  termed  slate,  a 
remarkable  durability.  Its  particles  are  laced 
together  by  a  network  of  parallel  films  of  micro- 
scopic crystals.  Slates  may  be  of  any  antiquity. 
Nothing  but  folding  and  uplifting  of  mountainous 
masses  is  needed  to  form  them.  In  England  and 
America  they  belong  chiefly  to  the  ancient  epochs 
of  time  distinguished  as  pre-Cambrian,  Cambrian, 
Silurian,  and  Devonian. 

Schists. —  The  transitions  between  slate  and 
schist  are  common  in  mountain  regions.  Crystals 
of  other  minerals  are  sometimes  developed  on  the 
cleavage  planes  of  slate.  Some  slates  are  very 
micaceous;  and  it  is  sometimes  difficult  to  say 
where  mica  slate  ends,  and  mica  schist  begins. 
The  original  bedding  is  usually  obliterated  in 
schists ;  so  that  the  rocks  give  no  evidence  of 
having  been  deposited  in  water.  Occasionally, 
as  in  the  mica  slates  south  of  Bergen  in  Norway, 
beds  of  limestone,  in  which  fossils  are  preserved, 
are  found  in  such  rocks.  In  the  north  of  Scot- 
land fossil-bearing  beds,  known  as  the  Durness 
limestone,  occur  between  schists,  where  they  are 
introduced  by  horizontal  dislocations. 

A  schist  presents  to  the  eye  an  arrangement  of 
short  irregular  layers  of  crystals,  which  is  similar 
to  the  appearance  which  a  thin  film  of  slate  shows 
under  the  microscope,  although  schists  differ  from 
slates  in  having  all  their  material  crystalline. 
There  is  some  reason  for  regarding  them  as  re- 
sults of  intenser  action  of  such  compression  as 
imparted  a  slaty  texture  to  ancient  beds  of  very 
varied  mineral  character. 


22  THE  STORY  OF   THE   EARTH. 

A  schist  thus  foliated  is  typically  an  alternation 
of  films  of  the  mineral  quartz  with  some  other 
minerals.  Each  quartz  film  is  made  up  of  a  num- 
ber of  crystals  matted  together,  and  occasionally 
little  plates  of  mica  separate  the  individual  crys- 
tals from  each  other.  The  mineral,  which  alter* 


FIG.  i. — Gneiss  :  showing  foliated  structure,  from  Gairloch  in 
Ross-shire. 

nates  with  the  quartz,  gives  its  name  to  the  schist, 
as  mica  schist,  hornblende  schist,  chlorite  schist. 
Some  schists,  such  as  gneiss,  are  identical  with 
granite  in  mineral  composition  ;  some  are  identical 
with  slates  in  chemical  composition.  Schists  are 
frequently  contorted  and  crumpled,  as  in  the  cliffs 
round  Holyhead,  with  a  minuteness  of  folding 
which  is  not  seen  in  slates.  Like  slates  they  can 
be  inferred  to  have  been  crystallized  by  the  trans- 
formation into  heat  of  the  pressure  which  elevated 
them.  They  have  been  exposed  at  the  surface  by 
removal  under  the  denuding  action  of  water,  of 
the  rocks  which  originally  covered  them. 

Schists  often  alternate  with  crystalline  quartz- 
rock,  wfrich  appears  to  have  been  originally  sand- 
stone, metamorphosed  by  partial  solution  and 


THE  MATERIALS  OF  MOUNTAIN   CHAINS.       23 

crystallization  which  has  blended  the  grains.  In 
some  localities,  as  on  the  west  coast  of  Scotland, 
limestone  occurs  in  schists  and  gneiss.  Its  tex- 
ture is  frequently  compact  and  crystalline,  and 
sometimes  saccharoid  like  statuary  marble.  It 
contains  many  minerals  but  no  fossils.  All  lime- 
stones were  originally  deposited  from  water. 
Thus  the  three  chief  types  of  water-formed  rock 
— sandstone,  clay  and  limestone — appear  to  be 
represented  among  schists.  The  process  which 
has  rendered  them  crystalline  is  termed  metamor- 
phism.  Metamorphic  rocks,  which  divide  into 
layers  by  differences  in  the  mineral  character  of 
their  crystalline  constituents,  are  said  to  be  foli- 
ated. This  foliation  may  be  regarded  as  closely 
comparable  with  the  cleavage  of  slates. 

Schists  may  be  formed  of  quartz,  felspar  and 
mica  in  parallel  layers,  when  the  rock  is  termed 
gneiss.  The  crystals  of  a  schist  may  be  thrown 
out  of  their  parallelism,  as  in  Anglesea,  so  as  to 
present  a  confused  mixture,  which  has  been 
termed  granite.  Some  observers,  however,  take 
the  converse  view,  and  believe  that  the  original 
texture  of  the  rock  was  granite,  and  that  the 
schistose  texture  has  been  acquired  by  shearing 
movement  acting  on  a  heated  plastic  rock.  In 
the  south  of  Cornwall  a  schistose  texture  has 
been  imparted  in  the  metamorphic  region  of 
Cornish  schists,  to  rocks  which  were  originally 
volcanic. 

Metamorphism  is  produced  in  several  distinct 
ways.  When  the  rocks  of  an  elevated  tract  be- 
come changed  in  texture  throughout  their  mass, 
the  expression  "  regional  metamorphism "  has 
been  used  to  distinguish  such  wide-spread  trans- 
formations of  rock  texture,  from  the  local  altera- 


24  THE  STORY  OF  THE  EARTH. 

tions  of  texture  termed  "contact  metamorphism," 
which  result  from  highly  heated  rocks  acting 
upon  the  sediments  over  which  or  through  which 
they  flow.  The  changes  produced  by  the  action 
of  the  atmosphere  and  infiltrating  water,  which 
break  up  minerals  originated  by  heat  or  pressure, 
and  elaborate  others  in  their  place,  give  rise  to 
"  sub-aerial  metamorphism." 

In  the  central  regions  of  mountain  chains,  such 
as  the  Grampians  and  the  central  axis  of  Devon 
and  Cornwall,  schists  sometimes  pass  into  the 
condition  termed  granite  ;  so  that  there  has  some- 
times seemed  to  be  a  relation  of  cause  and  effect 
between  the  position  in  which  the  granite  occurs, 
and  the  way  in  which  its  mineral  matter  is  ar- 
ranged. 

Granites  vary  so  much  in  the  minerals  they 
include  that  they  form  a  family  of  rocks  dis- 
tinguished by  chemical  and  mineral  composition 
and  texture.  The  minerals  depend  upon  the 
chemical  constituents.  The  silica  varies  from  55 
per  cent,  to  80  per  cent.  The  alumina  from  7 
to  20  per  cent.  So  that  the  quartz  is  commonly 
from  a  fifth  to  a  third  of  the  bulk  of  the  granite, 
though  occasionally  nearly  two-thirds.  The  mica 
may  occasionally  be  only  i  per  cent.,  though  it 
is  commonly  between  5  and  25  per  cent.  The 
felspars  form  between  40  and  70  per  cent,  of  the 
rock.  Sometimes  a  green  variety  of  hornblende 
gives  rise  to  hornblendic  granite.  Granite  may 
include  angular  fragments  of  schists,  slate  and 
limestone,  often  of  immense  size.  These  frag- 
ments appear  to  show  that  the  granite  is  intru- 
sive, and  that  it  tore  them  away  from  rocks 
through  which  it  passed.  Instances  have  been 
recorded  of  granite  resting  upon  schist.  Granite 


THE   MATERIALS   OF   MOUNTAIN   CHAINS.        25 

is  also  intruded  on  a  smaller  scale,  forming  veins, 
which  penetrate  into  other  rocks,  or  sometimes 
cut  through  the  granite  itself.  The  only  evidence 
of  the  condition  and  temperature  at  which  the 
granite  was  intruded  is  afforded  by  its  junction 
with  slate.  In  Cornwall,  where  the  slate  near  to 
it  has  acquired  the  texture  of  mica  schist  and 
gneiss,  there  is  no  evidence  to  show  whether  that 
metamorphism  was  due  to  the  heat  of  the  granite, 
or  to  the  pressure  which  it  exerted,  or  both  com- 
bined. 

A  few  rocks  which  are  found  in  mountain 
regions  resemble  granite  in  texture,  but  differ 
from  it  in  mineral  constituents,  owing  to  the 
original  chemical  difference  of  the  material  out 
of  which  the  crystals  are  formed.  Syenite  is  well 
known  in  Charnwood  Forest  and  in  Guernsey. 
Syenite  is  a  rock  formed  commonly  of  orthoclase 
felspar,  hornblende  and  black  mica.  They  are  a 
variable  group,  including  mica  syenites,  augite 
syenites,  nepheline  syenites,  zircon  syenites  and 
many  others. 

A  third  type  of  granite  rock  is  named  gabbro. 
It  is  familiarly  known  in  the  Cuchullin  hills  in 
Skye.  Its  crystals  are  as  large  as  those  of  granite, 
and  similarly  arranged.  It  is  formed  of  a  plagio- 
clase  felspar  like  labradorite,  associated  with  some 
mineral  of  a  brassy  or  metallic  aspect  like  diallage, 
and  often  contains  black  mica  and  olivine ;  and 
in  some  localities  hornblende. 

These  granitic  rocks  have  been  termed  plu- 
tonic  because  they  appear  to  originate  in  the  re- 
gion which  mythology  assigns  to  Pluto,  in  the 
interior  of  the  earth,  consolidating  slowly  under 
great  pressure. 


26  THE  STORY  OF  THE  EARTH. 

CHAPTER   IV. 

VOLCANIC    ROCKS. 

No  clear  distinction  can  be  drawn  between 
plutonic  rocks  and  coarsely  crystalline  forms  of 
volcanic  rocks.  Both  are  extruded  in  some  in- 
stances from  deep-seated  parts  of  the  earth.  In 
consequence  of  the  rigid  condition  of  the  globe 
it  is  impossible  that  those  rocks  came  to  the  sur- 
face from  an  unconsolidated  interior  by  ascend- 
ing fissures.  Many  writers  have  assumed  the 
existence  of  molten  areas  or  lakes  in  the  interior 
of  the  crust,  as  a  source  for  lava  streams,  which 
sometimes  flow  on  the  surface  for  a  hundred 
miles. 

Others,  again,  assume  that  the  longitudinal 
fissures,  along  which  volcanic  cones  have  been 
built,  penetrate  down  to  different  layers  of  the 
earth,  each  distinguished  by  having  the  mineral 
character  of  the  different  kinds  of  volcanic  rocks. 
Such  a  fissure  allows  the  atmosphere  to  penetrate 
downwards,  and  removes  from  the  heated  rock 
the  pressure  which  had  kept  it  solid.  The  rock 
then  liquefies  and  ascends  the  fissure  like  fluid  in 
a  pump,  until  it  comes  in  contact  with  water  de- 
rived from  the  earth's  surface,  and  so  generates 
steam,  which  forms  the  explosive  outbursts.  The 
steam  ascends  miles  high  into  the  air,  carrying 
up  the  rock  in  the  form  of  dust.  The  dust  from 
the  volcano  Krakatoa,  in  the  Strait  of  Sunda, 
ejected  in  1884,  remained  suspended  for  more 
than  a  year. 

On  this  hypothesis  the  difference  between 
plutonic  rocks  and  volcanic  rocks  is  in  the  circum- 


VOLCANIC   ROCKS.  27 

stance  that  the  plutonic  rocks  consolidate  deep 
in  the  earth,  while  the  volcanic  rocks  consolidate 
under  the  pressure  of  the  atmosphere,  or  near  to 
the  surface. 

The  principal  types  of  volcanic  rocks  are 
named  Rhyolites,  Trachytes,  Andesites  and  Ba- 
salts. The  basalt  has  been  supposed  to  be  the 
last  formed;  and  to  have  come  from  a  greater 
depth  than  the  others,  being  commonly  the 
densest  of  the  volcanic  rocks.  It  frequently  rests 
upon  andesites  and  rhyolites.  These  rocks  have 
been  repeated  several  times  in  succession  in  the 
history  of  the  earth.  Rhyolites  are  found  in  the 
old  pre-Cambrian  rocks  of  Wales;  andesites  in 
the  Cambrian  rocks  of  the  Lake  district,  and  the 
Old  Red  Sandstone  of  Scotland ;  while  in  the 
later  Coal  Measures  there  were  countless  out- 
bursts of  basalt.  The  volcanic  rocks  of  the  Ter- 
tiary period  in  Britain  are  a  repetition  of  those  of 
the  Primary  period,  basalts  succeeding  andesites 
and  rhyolites. 

There  is  at  the  present  day  something  like  a 
geographical  distribution  of  the  different  volcanic 
rocks.  The  volcanos  of  the  Andes  pour  out  the 
rock  named  andesite.  The  voleanos  of  Southern 
Italy  give  out  varieties  of  basalt.  Metals  are 
very  rarely  associated  with  volcanic  eruptions, 
though  an  appreciable  quantity  of  silver  has  been 
found  in  volcanic  ash  of  eruptions  in  Chili. 

Chemical  and  mineral  composition  alike  sug- 
gest the  closest  relation  between  the  deep-seated 
crystalline  rocks  and  those  which  flow  from  vol- 
canos. The  plutonic  granite  appears  to  become 
the  volcanic  rhyolite.  Plutonic  syenite  and  dio- 
rite  on  reaching  the  surface  appear  to  become 
andesite.  And  the  rock  which  cooling  under 


28        THE  STORY  OF  THE  EARTH. 

pressure  becomes   gabbro,  after  flowing  on   the 
earth's  surface  becomes  basalt. 

Rhyolite. — The  name  rhyolite  indicates  the 
fluidal  structure  of  the  cooled  lava,  which  results 
from  the  movement  of  minute  crystals  about 
larger  crystals  in  the  flow  of  the  molten  stream. 
Some  of  the  crystals  are  visible  to  the  eye.  The 
material  between  them  is  named  the  ground  mass. 
Under  the  microscope,  this  ground  mass  is  seen  to 
be  formed  of  microscopic  crystals,  with  an  un- 
crystalline  material  between  them,  distinguished 
as  the  base.  The  visible  crystals  are  principally 
quartz,  with  the  glassy  variety  of  orthoclase  fel- 
spar named  sanidine.  These  minerals  may  form 
the  entire  mass  of  a  granite  rhyolite.  But  rhyolite 
may  be  free  from  crystals,  forming  a  glass,  such 
as  obsidian;  or  be  expanded  into  a' froth  like 
pumice. 

Nearly  all  crystalline  rhyolites  are  full  of  con- 
cretions with  a  radiating  structure,  or  alternations 
of  granular  layers  with  spherulitic  layers,  and 
these  are  known  as  spherulites.  Besides  the 
common  form  of  quartz,  another  variety  named 
tridymite  occurs,  in  hexagonal  plates.  A  little 
mica  and  sometimes  hornblende  may  be  diffused 
in  the  rock.  The  oldest  British  volcanic  rocks  of 
St.  David's,  Bangor  and  the  Wrekin,  are  rhyolites. 
Rhyolites  and  rhyolitic  ashes  often  occur  around 
granitic  centres,  as  though  they  were  mutually 
related. 

Andesite. — Andesites  contain  55  to  75  per  cent. 
of  silica.  As  the  silica  increases,  the  percentage 
of  alumina  decreases  from  20  to  about  12  per 
cent.  The  oxide  of  iron  and  lime  also  become 
less  with  the  increase  of  silica.  Typical  andesites 
are  formed  of  oligoclase  felspar,  and  columnar 


VOLCANIC   ROCKS.  29 

hornblende,  in  a  glassy  ground  mass,  with  a  little 
mica  and  magnetic  iron.  The  quartz  hornblende 
andesites  correspond  to  syenites  in  chemical  com- 
position ;  just  as  syenites  correspond  chemically 
to  some  Cambrian  slates.  The  hornblende  ande- 
sites, which  are  free  from  quartz,  are  closely  re- 
lated to  the  rocks  named  diorites.  Andesites  are 
largely  quarried  on  the  Rhine,  in  the  Siebenge- 
birge,  near  the  Apollinaris  spring  at  Remagen. 
Andesite  abounds  in  black  concretions  rich  in 
hornblende,  like  those  found  in  the  granite  of 
Shap  in  Westmoreland.  Phonolite  is  probably  a 
volcanic  representative  of  a  syenite  which  con- 
tains the  mineral  nepheline. 

Basalt. — This  is  the  most  familiar  volcanic 
rock.  Its  silica  is  reduced  to  35  to  55  per  cent. 
Oxide  of  iron,  lime,  and  magnesia  are  more  abun- 
dant in  it  than  in  other  volcanic  rocks.  It  con- 
sists chiefly  of  the  minerals  labrador-felspar,  and 
augite,  or  some  similar  substance,  usually  associ- 
ated with  a  little  magnetite  and  olivine.  It  is 
dark  in  tint,  grey-brown,  blue-black,  or  greenish 
black  when  freshly  broken.  Cooled  slowly,  it 
gains  a  fine  granular  texture,  and  is  known  as 
dolerite.  * 

In  the  most  ancient  basalts  of  Cambrian, 
Silurian  and  Devonian  ages  the  olivine  and  augite 
have  been  partly  decomposed,  and  converted  into 
a  green  mineral  like  chlorite.  The  basalt  or 
dolerite  is  then  known  as  diabase.  The  less 
altered  dolerites,  of  carboniferous  age,  have  been 
termed  melaphyres.  Occasionally  the  felspar  in 
basalt  may  be  replaced  by  allied  minerals.  In 
Etna  and  Vesuvius  leucite  takes  its  place.  There 
is  also  a  nepheline  basalt. 

Olivine  may  take  the  place  of  felspar.     That 


30  THE   STORY   OF   THE   EARTH. 

mineral  then  gives  a  name,  peridotite,  to  the  rocks 
in  which  it  is  an  essential  constituent.  Those 
rocks  are  frequently  converted  by  decomposition 
into  serpentines. 

Volcanic  rocks  of  the  basalt  family  sometimes 
divide  into  beautifully  regular  six-sided  columns, 
such  as  are  familiar  in  the  island  of  Staffa,  and 
the  Giant's  Causeway  in  the  north  of  Ireland.  A 
lava  flow  sometimes  cools  from  its  floor  and  also 
from  its  upper  surface;  and  two  independent  sets 
of  vertical  columns  of  different  sizes  may  then  be 
formed,  separated  by  a  crystalline  part  in  the 
middle. 

Each  of  these  kinds  of  lava  may  also  be  repre- 
sented by  fragmental  rocks,  having  the  aspect  of 
cinders,  or  dust.  In  past  periods  of  geological 
time,  beds  of  volcanic  agglomerate,  of  ashes,  and 
vesicular  lavas  are  common  in  association  with 
compact  lavas.  In  North  Wales,  among  the 
Arenig  rocks,  the  ashes  are  enormously  thick  in 
Cader  Idris,  Aran  Mowddwy  and  Arenig  moun- 
tains, and  there  is  little  doubt  that  the  ash  was 
ejected  from  volcanic  throats  near  Dolgelly  and 
Arenig. 

In  the  Permian  rocks  near  Exeter,  the  beds  of 
volcanic  ash  at  Pocombe  are  manifestly  drifted 
by  the  wind.  And  at  Spence  Combe  the  lava  flow 
is  highly  vesicular,  with  the  vesicles  filled  with 
minerals,  giving  singular  evidence  of  elongation 
of  the  steam  cavities  by  flow  in  these  old  lavas  of 
Devonshire. 

There  is  a  close  chemical  resemblance  between 
the  several  types  of  volcanic  and  plutonic  rocks, 
and  a  marked  similarity  in  their  mineral  composi- 
tion, which  suggests  a  common  origin.  The  evi- 
dence is  not  quite  so  complete  that  would  tend  to 


.      THE   MATERIALS   OF   STRATA.  3! 

establish  a  transition  from  the  plutonic  rocks 
through  schists  to  water-formed  deposits.  It  has 
not  been  fully  collected,  but  deserves  examina- 
tion, since  the  earth  offers  no  indication  of  a  be- 
ginning in  its  geological  history.  If  metamor- 
phism  such  as  is  manifest  in  the  older  rocks  were 
extended  over  the  earth's  surface  it  would  oblit- 
erate records.  And  the  wearing  up  of  such 
metamorphosed  rocks  into  new  sediments  would 
ensure  a  succession  of  similar  rock  materials. 


CHAPTER   V. 

THE    MATERIALS    OF    STRATA. 

Terrestrial  Rocks. 

AROUND  many  parts  of  the  coast,  as  in  Lanca- 
shire and  Norfolk,  the  winds  blow  up  sands  from 
the  sea-bed,  laid  bare  at  low  tide.  These  sands 
form  low  ranges  of  hills,  known  as  sand  dunes. 
They  often  show  forms  of  hill  contours  as  varied 
as  are  produced  by  the  work  of  water  and  frost  in 
carving  hills  out  of  solid  material.  These  sand 
dunes  are  but  an  insignificant  illustration  of  the 
work  done  by  the  wind,  in  heaping  and  rounding 
the  grains  of  sand  which  form  desert  regions. 
There,  every  grain  of  quartz,  which  in  a  sandstone 
usually  retains  some  of  its  angles  of  crystal  form, 
is  rounded  by  long  continued  motion,  till  it  be- 
comes a  miniature  pebble.  There  is  some  evi- 
dence that  desert  conditions  not  altogether  dis- 
similar to  those  of  Arabia  or  the  Sahara  may 
have  existed  in  Great  Britain  at  the  beginning  of 
the  Secondary  period  of  time,  when  the  rock  salt- 


32  THE   STORY  OF  THE   EARTH. 

was  in  process  of  accumulation  by  the  evaporation 
of  land-locked  basins  of  the  sea.  In  Lancashire 
and  Cheshire,  in  the  lower  part  of  the  Trias,  there 
are  some  layers  known  as  the  "  millet  seed  beds  " 
because  the  separate  grains  of  sand  flow  between 
the  fingers  like  millet  seed  or  shot.  Those  minute 
pebbles  are  not  all  of  quartz  but  partly  of  felspar. 
They  can  only  be  compared  to  blown  sands  of 
deserts  in  their  pebble-like  forms. 

The  less  completely  rounded  sand  grains  in 
ordinary  sandstones  have  probably  acquired  their 
character  from  long  continued  rolling,  partly  in 
rivers,  partly  on  shores,  as  they  have  passed  from 
one  geological  deposit  to  another  in  successive 
epochs  of  time,  as  a  consequence  of  the  construc- 
tion of  new  layers  of  rock  out  of  the  materials  of 
ancient  lands;  a  process  repeated  again  and  again, 
and  still  in  progress. 

Another  terrestrial  rock  which  can  scarcely  be 
termed  water-formed,  because  it  is  accumulated  by 
vegetable  growth,  is  seen  in  the  peat,  which  cov- 
ers large  parts  of  the  earth's  surface  where  the 
mean  temperature  falls  belows  42°  F.  It  is  well 
known  that  peat  frequently  originates  in  the  fall 
of  forest  trees,  because  they  obstruct  the  surface 
drainage  on  level  lands,  until  bog  plants  grow  and 
form  a  sponge-like  covering  to  the  land  which 
buries  the  fallen  trees,  and  kills  the  adjacent  for- 
est. Such  accumulations  in  Cambridgeshire  have 
been  stated  to  attain  a  thickness  of  40  feet.  In 
the  East  of  England,  as  in  Ireland,  there  are  two 
successive  peats.  The  older  has  yew  trees  at  the 
base  ;  and  the  newer  peat  covers  forests  of  pine 
trees.  In  the  Fens  of  the  Isle  of  Ely  these  peats 
are  often  separated  by  a  clay  of  marine  origin, 
the  "  buttery  clay  "  of  the  Fen-man,  the  Scrobicu- 


THE   MATERIALS   OF   STRATA.  33 

taria  clay  of  science,  so  named  from  a  bivalve 
shell  found  in  it,  which  lives  in  the  swampy  inlets 
on  the  east  coast  of  England.  In  that  clay  are 
occasionally  found  the  remains  of  walrus  and 
seal,  whale  and  grampus  ;  showing  that  the  inlet 
known  as  the  Wash  extended  southward  during 
the  deposition  of  the  clay,  over  the  lower  peat  in 
much  of  the  Isle  of  Ely.  When  peat  becomes 
compressed  by  the  deposition  of  superincumbent 
rock,  it  is  consolidated  like  the  rocks  with  which 
it  alternates.  There  are  important  geological  de- 
posits, which  have  grown  in  the  same  way,  in  the 
successive  periods  of  time.  At  the  beginning  of 
the  tertiary  period,  at  Bovey  Tracey  in  Devonshire, 
alternations  of  lignite  and  clay  form  a  succession 
of  layers  which  fill  up  a  lake-basin  in  the  older 
rocks :  similar  growths  are  seen  in  the  Brack- 
lisham  beds  of  the  Isle  of  Wight.  In  the  second- 
ary rocks  there  is  a  remarkable  bed  of  vegetable 
matter  five  feet  thick,  at  Brora  in  Sutherland, 
which  is  worked  for  coal.  Thinner  beds  are  found 
on  the  Yorkshire  coast,  which  appear  to  have 
grown  like  the  modern  beds  of  peat,  in  the  posi- 
tions in  which  they  are  found.  Far  more  impor- 
tant are  the  beds  of  consolidated  vegetable*matter 
found  in  the  upper  carboniferous  rocks  of  the  pri- 
mary period,  which  are  commonly  known  as  coal. 
They  often  give  evidence  of  change  in  level  of 
land  during  their  accumulation;  the  same  bed 
being  thick  in  one  place  and  divided  up  at  a 
little  distance  by  intervening  sedimentary  de- 
posits. These  accumulations  of  sediments  pre- 
serve indications  of  the  plant  life  of  the  earth, 
and  in  the  associated  sediments  are  occasional- 
ly found  remains  of  insects  and  other  terrestrial 
animals  which  lived  in  the  same  epochs  of  time. 


34        THE  STORY  OF  THE  EARTH. 


Pebble  Beds. 

Any  rock  which  is  sufficiently  durable  to  break 
into  compact  pieces  may  give  rise  to  a  pebble  bed 
when  the  fragments  are  further  reduced  in  dimen- 
sions by  the  action  of  frost,  or  the  transporting 
movement  of  a  flowing  river,  or  the  battering  ac- 
tion of  waves  upon  a  shore  or  shoal.  The  harder 
rocks  are  not  rounded  into  pebbles  without  long 
continued  rolling.  The  term  pebbles  is  applied 
to  stones  more  than  half  an  inch  in  diameter,  so 
that  they  vary  in  size  from  Barcelona  nuts  to  co- 
coanuts.  Stones  which  are  larger  than  these  are 
termed  boulders.  Stones  which  are  smaller  are 
often  termed  grits.  A  river  flowing  two  miles  an 
hour  transports  stones  as  large  as  eggs,  so  that 
pebbles  may  be  brought  by  such  means  from 
many  kinds  of  rock  which  are  exposed  in  the  in- 
terior of  a  country.  They  are  mixed  and  ac- 
cumulated either  on  shores,  or  where  the  stream 
leaves  them  behind  owing  to  its  slower  move- 
ment. 

The  pebble  beds  around  shores  are  carried 
backwards  and  forwards  with  the  daily  movement 
of  the  tidal  waters,  and  they  serve  to  mark,  when 
covered  up  by  other  sediments,  ancient  shores  of 
seas  which  existed  in  bygone  time.  Pebbles 
which  exist  in  the  old  geological  deposits  have 
been  derived  from  granites  and  schists,  from  con- 
solidated quartz  rock,  and  lava  streams,  from  con- 
solidated sandstones,  and  veins  of  quartz  which 
infiltrating  waters  have  deposited  in  the  cracks 
which  upheaval  has  produced  in  ancient  slates. 
Many  beds  of  pebbles  have  been  formed  from  con- 
cretions of  flint,  and  similar  substances,  which 


THE   MATERIALS   OF  STRATA. 


35 


FIG.  2. — Conglomerate  of  flint-pebbles,    from  the   Hertfordshire 
puddingstone,  showing  the  external  surface  of  the  pebbles. 


FIG.  3. — Fracture  through  this  conglomerate,  showing  sections  of 
flint-pebbles  imbedded  in  a  siliceous  cement. 


36  THE   STORY  OF   THE   EARTH. 

prove  more  durable  than  the  geological  deposits 
in  which  they  were  contained. 

Pebble  beds  indicate  the  ceaseless  action  of 
water  in  wasting  the  earth's  surface,  which  has 
gone  on  without  intermission  through  all  the 
periods  of  past  time,  because  tides  have  never 
ceased  to  flow  and  ebb  or  rivers  to  run. 

The  positions  in  which  pebble  beds  accumulate 
have  changed,  because  the  outlines  of  the  seas 
alter  with  the  folding  of  the  rocks  during  past 
ages;  and  they  frequently  come  back  again  age 
after  age  with  variation  in  level  of  land,  at  long 
intervals  to  be  re  deposited  upon  a  shallow  sea- 
bed, or  shore-line  in  the  same  district. 

Occasionally  the  pebbles  are  scratched,  and 
some  in  the  Permian  rocks  of  Worcestershire  are 
regarded  as  ice-worn  fragments. 

The  pebbles  are  frequently  bound  together  by 
a  cement,  which  converts  a  loose  aggregate  of 
stones  into  a  compact  and  durable  rock.  The 
most  important  of  these  cements  is  silica  which  is 
occasionally  more  durable  than  the  pebbles  which 
it  binds  together,  as  may  be  seen  in  the  Hert- 
fordshire puddingstone.  Such  rocks,  named  con- 
glomerates, are  also  formed  of  pebbles  bound 
together  with  a  cement  of  oxide  of  iron,  or  of  car- 
bonate of  lime. 

Conglomerates  and  pebble  beds  are  among 
the  oldest  known  geological  deposits  in  Britain. 
Among  the  primary  rocks  they  are  formed  almost 
entirely  of  granite,  schists,  and  lavas.  Among 
the  secondary  rocks  the  pebbles  which  make  up 
conglomerates  are  frequently  derived  from  rocks 
that  have  more  obviously  had  a  water-formed 
origin.  In  the  tertiary  period  of  time  most  of  the 
English  pebble  beds  have  been  derived  from  the 


THE   MATERIALS   OF   STRATA.  37 

grinding  up  of  flints,  liberated  from  the  destruc- 
tion of  the  chalk. 

Pebble  beds  frequently  mark  important  divi- 
sions of  geological  time  in  the  country  in  which 
they  are  found;  because  their  existence  implies 
that  change  of  level  of  land  which  resulted  in  the 
tidal  denudation  which  brought  them  into  exist- 
ence. Among  examples  of  great  pebble  beds  and 
conglomerates  may  be  mentioned  the  geological 
deposit  known  as  the  Llandovery  beds,  which  in 
Wales  forms  the  base  of  the  true  Silurian  rocks, 
and  extends  successively  over  the  upturned  edges 
of  the  older  Cambrian  rocks,  which  had  previously 
been  planed  level  by  the  sea. 

* 

Sands. 

There  is  a  rapid  gradation  between  pebble- 
beds  and  sands.  Beds  of  intermediate  texture, 
with  many  grains  as  large  as  peas,  are  named 
grits,  and  are  typically  seen  in  some  layers  of  the 
"  Millstone  grit,"  which  underlies  the  coal.  The 
grains  are  miniature  pebbles,  often  angular,  formed 
by  rounding  angular  masses  of  quartz  rock  on  a 
sea  shore.  On  a  sandy  shore,  like  that  6f  Hast- 
ings, Reculvers  or  Hunstanton,  the  sands  now 
being  deposited  are  derived  from  sandstones 
which  form  the  cliffs,  broken  up  first  by  joints, 
and  afterwards  separated  into  grains,  similar  to 
the  material  out  of  which  such  sandstones  were 
originally  consolidated.  Cambridge  green  sand 
and  Neocomian  sand  contain  many  rock  frag- 
ments and  fossils  derived  from  ancient  deposits. 

The  particles  of  quartz  are  often  crystalline, 
but  are  sometimes  derived  from  uncrystalline 
forms  of  silica  such  as  chalcedony,  chert,  opal, 


38        THE  STORY  OF  THE  EARTH. 

and  flint.  Under  the  microscope  the  source  of 
the  grains  can  usually  be  recognised;  for  if  the 
quartz  was  originally  crystalline  all  the  crystal 
faces  are  rarely  lost,  and  the  mineral  may  include 
hair-like  crystals  of  other  minerals,  or  minute 
cavities  in  which  there  may  be  fluid  with  a  bubble 
of  air.  This  is  enough  to  show  that  the  quartz 
came  originally  from  the  wearing  away  of  schists 
or  granitic  rocks,  in  times  when  the  level  of  the 
land  caused  those  rocks  to  be  exposed  to  the  de- 
stroying influence  of  the  waves.  But  although  a 
sandstone  is  mainly  formed  of  quartz,  it  rarely 
contains  more  than  from  50  to  85  per  cent,  of 
silica — the  whole  of  which  is  not  in  the  crystalline 
form  of  quartz.  There  are  frequently  in  a  sand 
grains  of  water-worn  felspar.  The  felspar,  which 
is  a  silicate  of  alumina  combined  with  a  silicate  of 
soda  or  potash,  may  decompose,  liberating  the 
soluble  silicate  of  soda  or  potash.  Felspar  crys- 
tals abound  in  the  old  Cambrian  sandstones  of 
Barmouth,  in  the  Devonian  sandstones  of  South 
Devon,  and  in  the  Trias  sandstones  of  the  South 
of  England.  Sandstones  often  contain  scales  of 
the  mineral  mica,  as  in  the  Yorkshire  sandstones, 
used  for  paving.  Sometimes  the  mica  decays,  and 
then  the  iron  oxide  which  was  one  of  its  constitu- 
ents, gives  a  rusty  colour  to  the  sandstone.  Many 
sandstones  are  mainly  the  grains  of  quartz,  which 
were  constituents  of  crystalline  rocks,  liber- 
ated by  the  decay  of  minerals  with  which  they 
were  associated,  and  left  behind  comparatively 
near  to  the  source  from  which  they  were  derived. 
The  finer  particles  associated  with  them  which 
resulted  from  the  decomposition  of  other  minerals 
have  been  carried  to  greater  distances.  A  stream 
flowing  three  miles  an  hour  at  its  bottom  carries 


THE  MATERIALS  OF  STRATA.  39 

away  sand ;  but  sand  may  be  carried  out  to  a  dis- 
tance of  more  than  50  miles  from  the  shore.    The 


FIG.  4.— Laminated  vertical  sand  (Bagshot  sand)  of  Alum  Bay  in 
the  Isle  of  Wight,  showing  current  bedding.  •* 

size  of  the  particles  of  sand  when  coarse  is  -fo  of 
an  inch  ;  but  the  majority  of  the  grains  vary  from 
•j-J-g-  of  an  inch  to  y^j-gr  of  an  inch  in  diameter. 

When  a  sand  is  laid  down  it  is  incoherent.  It 
often  shows  evidence  of  its  shallow-water  origin, 
in  the  manner  in  which  currents  have  brought  its 
materials  from  different  directions.  After  a  de- 
posit of  sand  is  uplifted,  and  exposed  to  the  action 
of  rain-water  flowing  through  it,  it  begins  to  be 
bound  together  by  a  cement  which  determines  its 


40  THE  STORY  OF  THE   EARTH. 

durability.  There  are  three  chief  kinds  of  ce- 
ment, which  were  originally  of  vegetable  or  ani- 
mal origin.  First,  there  is  the  iron  sand  which  is 
commonly  red,  yellow,  or  brown  ;  and  is  rarely 
green.  The  iron  was  probably  collected  from  the 
sea-water  by  the  growth  of  marine  plants,  and 
liberated  by  their  decay.  Oxide  of  iron  is  liable 
to  accumulate  in  the  planes  in  which  water  has 
flowed  underground  through  the  rock,  which  are 
sometimes  determined  by  strain.  Examples,  of 
sand  so  coloured  are  seen  in  the  Bagshot  beds  of 
Alum  Bay,  in  the  Isle  of  Wight ;  and  the  Wealden 
beds  of  Warbarrow  Bay,  in  the  Isle  of  Purbeck. 
The  Wealden  sands  of  Kent  and  Sussex  are  so  rich 
in  iron  that  they  were  for  a  long  time  the  main 
source  of  the  metal  out  of  which  English  imple- 
ments of  war  and  ornaments  of  art  were  made. 

Sands  are  often  bound  into  calcareous  sand- 
stones by  a  cement  of  carbonate  of  lime.  It  is 
sometimes  derived  originally  from  the  evapora- 
tion of  water,  but  more  frequently  from  the  fall- 
ing to  the  bottom  of  organisms  which  lived  in  the 
water,  or  by  the  accumulation  of  marine  shells. 
The  Kentish  Rag,  which  forms  the  lower  part  of  the 
Lower  Greensand,  is  a  familiar  example  of  a  cal- 
careous sandstone  in  the  S.  E.  of  England.  The 
shells  become  dissolved  by  water  flowing  through 
the  rock  ;  and  the  carbonate  of  lime  of  which  they 
consisted  is  re-deposited,  so  as  to  fill  the  inter- 
spaces between  the  grains  of  quartz,  and  form 
crystals  which  bind  the  sand  into  a  sandstone. 

The  third  kind  of  sandstone  as  modified  by 
the  cementing  material  is  the  siliceous  sandstone, 
in  which  the  grains  of  quartz  are  bound  together 
by  silica..  These  sandstones  are  of  all  geological 
ages.  The  material  of  the  cement  appears  to  be 


THE   MATERIALS  OF  STRATA.  41 

in  most  cases,  if  not  always,  the  minute  particles 
of  the  siliceous  skeletons  of  sponges,  some  of 
which  resembled  the  Euplectella  speciosa  from 
eastern  seas,  sometimes  known  as  Venus's  flower 


FIG.  5. — Ripple-marked  sandstone  from  Permian  Rocks  in  the 
Karoo,  near  Prince  Albert,  Cape  Colony. 

basket.  The  spiculae  which  form  the  skeletons 
of  such  sponges,  dissolved  by  the  water  draining 
through  the  rock,  furnished  a  cement  which  is 
deposited  in  the  same  way  as  the  cement  of  cal- 
careous sandstones.  Infiltration  of  this  silica 
frequently  builds,  within  the  sandstone,  compact 
layers  of  a  flinty  rock,  known  as  chert.  Such 
layers  are  found  in  the  Lower  Greensand,  the 
Upper  Greensand,  and  especially  in  the  Carbon- 
iferous Limestone.  In  the  S.  E.  of  England  the 
sands  and  sandstones,  secondary  and  tertiary,  are 
often  coloured  green,  with  the  mineral  glaucon- 
ite.  As  a  rule  sands  are  red,  yellow,  or  brown, 


42  THE  STORY  OF  THE   EARTH. 

coloured  with  oxides  of  iron.  They  are  shallow- 
water  or  shore  deposits  which  show  current  bed- 
ding; due  to  deposition  by  changing  currents,  as 
well  as  ripple-marks  of  wave  movement,  and  foot- 
prints of  animals. 

Clay. 

Any  substance  which  is  taken  up  by  moving 
water  so  as  to  cloud  it,  is  popularly  termed  mud, 
and  mud  when  deposited  consolidates  into  clay. 
Mud  banks  abound  on  parts  of  the  coast  where 
clay  forms  the  cliffs,  because  tidal  movement  of 
the  water  converts  the  clay  into  mud.  It  is 
chiefly  composed  of  light  flocculent  particles  of 
silicate  of  alumina,  which  frost  tears  apart  from 
each  other,  and  the  lightest  shower  moves  down 
a  valley.  The  mud  of  rivers  is  carried  into  the 
sea,  as  far  as  the  fresh  water  can  float  over  the 
ocean.  The  Yellow  Sea  is  yellow  with  the  mud 
of  the  Hoang-Ho.  When  the  Rhine  at  Bonn  is 
turbid  and  full  of  water,  -%-fa$  part  of  its  weight 
is  mud;  but  after  continued  dry  weather  the  sedi- 
ment falls  to  -g-tf^nr  part  of  the  weight.  Thus  the 
alternation  of  seasons  may  give  a  laminated  char- 
acter to  deposits  carried  to  the  sea,  marking  the 
succession  of  years  by  changes  in  the  deposit,  like 
the  rings  of  growth  in  the  wood  of  a  tree. 

When  clay  extends  parallel  to  a  shore,  in  con- 
sequence of  denudation  of  the  cliffs,  it  commonly 
has  a  definite  relation  to  coarser  sediments  which 
are  deposited  nearer  to  land.  This  is  seen  in  the 
large  percentage  of  sand,  sometimes  amounting 
to  50  or  60  per  cent.,  which  may  be  separated 
from  clays  by  washing.  The  particles  of  sand 
however  are  extremely  fine,  so  that  they  are  held 
in  suspension  for  a  long  time  by  moving  water. 


THE   MATERIALS  OF  STRATA.  43 

Under  such  circumstances,  the  chemical  composi- 
tion of  a  clay  is  sometimes  the  same  as  that  of  a 
sandstone;  and  there  maybe  an  unbroken  tran- 
sition from  one  deposit  to  the  other  through  an 
intervening  loam.  Almost  all  the  minerals  which 
enter  into  the  composition  of  crystalline  rocks, 
are  occasionally  found  in  clays.  Often  the  origin 
of  a  clay  is  revealed  in  the  abundance  of  the 
flakes  of  mica  which  are  scattered  through  it,  for 
the  silicate  of  alumina  corresponds  chemically 
with  decomposed  felspar,  and  the  presence  of 
particles  of  quartz  diffused  in  it,  shows  that  the 
rock  has  been  derived  from  an  old  crystalline 
material.  The  presence  of  mica  renders  it  prob- 
able that  the  schists  which  were  denuded  were  of 
the  kind  termed  gneiss,  if  the  crystalline  rock 
was  not  granitic.  Some  ancient  clays  have  been 
found  full  of  needles  of  the  mineral  rutile.  The 
purest  clays  are  formed  on  land  from  the  decom- 
position of  white  granite.  Such  a  source  would 
appear  to  be  necessary  for  the  beds  of  white  pipe 
clay,  found  interstratified  in  the  Bagshot  sands  of 
-Hampshire  and  Dorset. 

The  colours  of  clay  are  due  to  oxides  of  iron. 
Occasionally,  as  in  the  Woolwich  and  Reading 
beds  at  Reading,  current  bedding  is  marked  by 
alternate  layers  of  red  and  green  clay.  Such  bed- 
ding would  be  unsuspected,  but  for  the  colour. 
Often  a  blue  clay  passes  into  a  brown  or  yellow 
tint.  It  is  then  sandy  and  porous,  so  as  to  per- 
mit the  infiltration  of  water  charged  with  atmos- 
pheric air,  which  oxidises  the  iron. 

Minor  sources  for  clay  are  the  small  percent- 
age of  silicate  of  alumina  which  is  the  insoluble 
residue  left  when  limestones  have  been  dissolved. 
This  forms  the  red  cave  earth  in  limestone  dis- 


44        THE  STORY  OF  THE  EARTH. 

tricts;  and  the  red  soil  on  limestones.  Beds  of 
volcanic  ash,  exposed  upon  the  surface,  may  be- 
come broken  up  by  atmospheric  decomposition 
and  converted  into  clay. 

The  bedding  of  clays  is  frequently  marked  by 
the  occurrence  of  thin  layers  of  earthy  limestone, 
or  of  concretions  termed  septaria,  which  are  dis- 
tributed in  parallel  layers,  on  zones  where  car- 
bonate of  lime  was  abundant.  These  concretions 
probably  mark  near  approach  to  the  limit  to  which 
the  ancient  mud  was  carried  in  the  sea,  where  the 
sediment  was  becoming  replaced  on  the  ocean 
floor  by  calcareous  layers  of  organic  origin.  The 
septaria  often  contain  upwards  of  50  per  cent,  of 
carbonate  of  lime,  and  their  occurrence  appears 
to  mark,  either  oscillations  in  level  of  the  sea  bed 
which  varied  the  distance  to  which  sediment  was 
carried,  or  indicates  that  the  land  area  which  was 
being  worn  away  to  form  the  new  deposit  became 
more  calcareous. 

One  of  the  most  interesting  clay  deposits  in 
England  is  the  inflammable  clay,  known  as  Kim- 
eridge  clay,  found  in  Lincolnshire  and  Cambridge- 
shire as  well  as  on  the  Dorset  coast.  Some 
layers  of  this  clay  when  distilled  yield  as  much  as 
40  per  cent,  of  paraffin,  naphtha,  tar  and  heavy 
oils,  which  are  similar  to  products  of  coal  tar. 
Those  chemical  substances  derived  from  coal  be- 
ing of  vegetable  origin,  it  is  probable  that  the  in- 
flammable character  of  the  clay  is  due  to  the  growth 
of  marine  algae,  though  no  traces  of  plant  remains 
are  found  among  the  remains  of  marine  shells 
which  crowd  the  deposit.  . 

Almost  all  clays  yield  the  minerals,  iron  pyrites, 
and  selenite,  which  are  closely  dependent  upon 
each  other.  Iron  pyrites  mineralizes  fossils,  and 


THE  MATERIALS  OF  STRATA.  45 

occurs  in  irregular  masses.  Both  iron  and  sulphur 
may  have  been  liberated  in  the  decay  of  marine 
plants.  As  the  iron  pyrites  decomposes  in  con- 
tact with  the  air,  its  sulphur  is  converted  into  an 
acid,  which  dissolves  the  substance  of  shells,  ex- 
pelling the  carbonic  acid,  and  forming  a  hydrated 
sulphate  of  lime,  known  as  selenite.  Occasion- 
ally phosphate  of  lime  form  concretions  in  clays 
and  mineralizes  fossils.  Clays  are  commoniy 
formed  in  deeper  water  than  sands,  and  further 
from  the  shores  which  furnished  the  sediment. 

Limestone. 

Limestones  differ  from  other  water-formed 
rocks  in  not  being  sediments.  Their  particles 
have  grown,  as  portions  of  organisms ;  and  have 
become  rock  substance,  when  the  animals  or 
plants  died,  which  separated  the  carbonate  of 
lime  from  water.  Sometimes  limestone  is  pre- 
cipitated by  evaporation  of  water.  The  carbonate 
of  lime  which  forms  limestones  is  usually  in  the 
mineral  condition  of  calcite. 

Beds  of  limestone  may  be  deposited  over  the 
whole  sea-bed,  whether  the  water  is  shattow  or 
deep.  As  a  rule  they  are  most  noticeable  in  the 
open  ocean,  beyond  the  limits  to  which  sediments 
are  carried.  Limestone  may  be  formed  near  into 
shore ;  and  when  the  rock  is  dissolved  away  by 
acids,  in  some  cases  nothing  remains  but  a  vary- 
ing percentage  of  siliceous  sand.  Rocks  of  that 
kind  are  termed  calcareous  grits. 

Evidences  of  the  shallow- water  origin  of  some 
oolitic  limestones  in  the  west  of  England,  are  also 
seen  in  current  bedding,  which  characterizes  some 
oolitic  rocks,  and  is  as  marked  as  in  sandstones. 


46  THE   STORY  OF  THE   EARTH. 

The  limestones  named  oolites,  are  probably  all 
formed  in  moderate  depth  of  water ;  since  there  is 


FIG.  6. — Lithographic  limestone  from  Solenhofen,  showing  circular 
staining  at  the  intersection  of  rectangular  joints ;  and  corru- 
gated fracture  on  the  right  side. 

some  evidence  to  show  that  the  oolitic  grains  may 
be  derived  from  plants  like  the  Nullipores,  and 
larger  grains,  termed  Pisolite,  show  a  minute 
tubular  structure,  attributed  to  an  organism 
named  Girvanella. 

Beds  of  shell  limestone  are  seen  in  process  of 
formation  on  many  shores.  Shell-haven,  in  the 
Thames,  takes  its  name  from  the  manner  in 
which  shells  are  drifted  together  so  as  to  form  a 
deposit ;  and  a  similar  accumulation  may  be  ob- 


THE  MATERIALS  OF  STRATA.  47 

served  at  Shell  Ness  which  makes  the  eastern  end 
of  the  Isle  of  Sheppey.  Parts  of  the  forest  mar- 
ble in  Oxfordshire,  consist  of  accumulated  growths 
of  shells;  and  in  Gloucestershire  portions  of  the 
same  deposit  show  ripple  marks  which  indicate 
shallow  conditions  of  deposition. 

Coral  reefs  are  also  to  be  classed  as  shallow- 
water  limestones  since  the  coral  grows  most  vigor- 
ously where  the  water  is  aerated  by  the  movement 
of  the  waves  near  to  the  surface  of  the  sea.,,  The 


FIG.  7. — Carboniferous  limestone,  the  surface  dissolved  by  rain, 
showing  the  remains  of  Encrinite  columns,  of  which  it  is  part- 
ly formed. 

great  brainstone  coral  Meandrina  and  the  com- 
pact coral  Forties,  associated  with  Nullipores 
build  buttresses  which  constitute  the  living  foun- 
dation of  the  reef.  Our  English  coral  limestones 


48  THE   STORY   OF   THE   EARTH. 

all  give  evidence  of  shallow-water  conditions, 
exactly  such  as  are  seen  in  the  growths  of  fring- 
ing reefs  of  coral  at  the  present  day. 

There  is  a  second  group  of  limestones  which 
may  be  termed  oceanic,  or  deep-sea  limestones, 
made  known  by  exploration  of  the  floors  of  the 
great  oceans.  They  are  largely  composed  of  the 
minute  organisms  termed  foraminifera,  such  as 
cover  so  much  of  the  Atlantic,  Pacific  and  Indian 
oceans.  Among  geological  deposits  due  to  such 
organisms,  may  be  placed  the  Chalk  of  Europe ; 
the  Nummulitic  limestone,  which  extends  through 
Europe,  Africa,  and  Asia ;  and  the  Fusulina  lime- 
stone, which  extends  from  Russia  to  Japan. 

There  are  other  animals  which  appear  to  form 
deep-water  limestones,  since  they  live  in  some 
depth  of  water  at  the  present  day,  such  as  the 
group  of  shells  termed  Brachiopoda;  and  Encri- 
nites,  which  make  up  portions  of  the  Carbonifer- 
ous Limestone  in  this  country. 

An  oceanic  limestone  is  not  necessarily  built 
tip  in  deep  water,  although  such  rocks  often  attain 
a  great  thickness.  It  is  only  necessary  that  the 
sea  in  which  the  rock  accumulates  should  be  be- 
yond the  limits  to  which  sediments  from  land  can 
be  transported.  Ocean  basins  often  increase  in 
depth  as  the  deposit  increases  in  thickness,  when 
limestones  may  be  formed  as  thick  as  are  the 
Carboniferous  limestone  of  Flint  and  Derbyshire. 

Fresh  Water  Deposits. 

Accumulations  of  sands,  clays,  and  limestones 
are  brought  down  from  higher  land  wherever 
fresh  waters  accumulate  upon  the  land  surface 
If  the  pond  or  lake  rests  upon  a  limestone  the 


THE   MATERIALS   OF   STRATA.  49 

deposits  formed  within  the  lake  will  be  mainly 
calcareous.  Fresh-water  plants  like  the  Chara 
precipitate  carbonate  of  lime  upon  the  stem  by 
absorbing  the  carbonic  acid  gas  from  the  water, 
so  that  the  carbonate  of  lime  is  no  longer  soluble. 
This  ensures  an  accumulation  of  granular  lime- 
stone as  the  plants  decay.  Such  a  deposit  covers 
up  the  remains  of  fresh  water  shells,  and  fre- 
quently the  remains  of  animals  derived  from  tand. 

The  lakes  in  Cumberland  and  Westmoreland 
are  found  to  have  their  beds  covered  with  deposits 
which  consist  of  volcanic  minerals  when  they  lie 
in  regions  occupied  by  old  volcanic  rocks ;  while 
the  deposits  are  ordinary  sediments  when  the 
lakes  are  surrounded  by  rocks  formed  of  such  ma- 
terials. If  the  lake  is  sufficiently  large,  like  the 
Lake  of  Geneva,  the  sediments  may  be  completely 
sorted,  successively  deposited,  and  pass  from  the 
condition  of  coarse  pebbles  and  boulders  where 
the  Rhone  coming  from  the  Valais  enters  the  lake, 
to  the  finest  sediment  where  its  clear  waters  leave 
it,  southward  of  Geneva.  Hence  a  lake  may  con- 
tain an  epitome  of  all  known  water-formed  rocks 
— pebble-beds,  sands,  clays,  limestones — as  well 
as  layers  of  plant  remains  consolidated  into 
lignite. 

Examples  of  such  fresh-water  growth  of  sedi- 
ments alternating  with  lignite,  has  been  already 
referred  to  in  the  layers  known  as  Coal  Measures. 
In  the  lacustrine  deposits  which  are  so  important 
in  the  northern  part  of  the  Isle  of  Wight,  fresh- 
water limestones  are  familiarly  seen  at  Headon 
Hill  and  Bembridge,  which  were  formed  in  fresh- 
water lakes,  and  give  no  evidence  of  sediments 
being  mixed  with  the  calcareous  matter.  Other 
fresh-water  limestones  alternating  with  terrestrial 


50  THE  STORY  OF  THE   EARTH. 

surfaces,  on  which  the  remains  of  coniferous  forest 
trees  stand  erect,  are  seen  in  the  Purbeck  beds  of 
the  Isle  of  Portland  and  the  Isle  of  Purbeck  in 
Dorsetshire.  Fresh-water  sediments,  alternations 
of  sands  and  clays  are  found  with  numerous  rep- 
etitions in  the  Wealden  beds  of  the  Isle  of  Purbeck, 
and  the  Isle  of  Wight ;  and  they  are  associated 
into  a  few  deposits,  fairly  well  defined  into  sands 
and  clays,  in  the  Wealden  strata  of  Kent  and 
;  Sussex. 

Recognition  of  the  fresh-water  origin  of  all 
such  rocks  rests  upon  the  presence  in  them  of 
animals  which  lived  in  fresh  water.  When  these 
are  shells  they  are  often  matted  together  to  form 
layers  of  some  thickness.  The  types  or  genera 
are  identical  with  those  which  live  in  every  pond, 
lake  and  stream  on  the  surface  of  the  country  at 
the  present  day.  The  bivalve  shells  are  usually 
species  of  Cyclas,  or  Unio,  or  Anodonta.  The  uni- 
valve shells  are  either  the  pond  shells  Planorbis, 
Paludina  and  Limncza,  or  such  river  shells  as  Neri- 
tina,  and  the  fresh-water  limpet. 

There  is  probably  no  fresh-water  limestone 
from  which  the  seed-vessels  of  the  plant  Chara 
are  absent.  Sometimes  the  presence  of  the  sili- 
ceous spiculae  of  the  fresh-water  sponge,  Spongilla, 
has  resulted  in  fossils  being  mineralized  with  silica, 
as  in  the  Purbeck  beds,  or  the  formation  of  sili- 
ceous layers  and  concretions  in  fresh-water  lime- 
stones, which  may  be  compared  to  the  veins  and 
concretions  of  flint  found  in  marine  strata  like  the 
Chalk  and  Carboniferous  Limestone. 


THE  SUCCESSION   OF  STRATA.  51 

CHAPTER   VI. 

THE    SUCCESSION    OF    STRATA. 

Contemporaneous  origin  of  water-formed  rocks. 

THE  conditions  under  whjch  sediments  grad- 
ually become  finer,  as  the  distance  from  shore  and 
depth  of  water  increase,  show  that  all  known 
varieties  of  rock  may  be  formed  and  deposited 
adjacent  to  each  other  at  the  same  time.  Not 
only  are  the  beds  of  peat  in  Irish  bogs  contem- 
poraneous with  the  shell  marls  in  the  loughs,  but 
these  are  contemporaneous  with  the  sands,  clays, 
and  limestones  which  are  forming  at  the  present 
time  in  our  seas.  Any  one  type  of  mineral  mat- 
ter may  be  represented  by  all  the  other  types  of 
which  layers  of  rock  can  be  formed,  in  a  succes- 
sion of  different  localities.  A  geological  period 
of  time  may  be  as  accurately  represented  by  ter- 
restrial lignite,  or  fresh-water  sands,  as  by  any 
kind  of  marine  deposit.  The  chalky  muds  dredged 
a  few  hundred  miles  west  of  Ireland  are  accumu- 
lated in  deeper  water  in  association  with  different 
types  of  life,  but  manifestly  formed  contempo- 
raneously with  the  shell  beds  of  Shell  Ness,  the 
muds  carried  out  by  the  Thames,  and  the  sands 
which  are  spread  by  the  tides  off  Yarmouth. 

In  all  geological  ages  there  has  been  the  same 
contemporaneity  of  rocks  of  different  mineral 
character.  Marine  rocks  must  have  been  laid 
down  at  the  same  time  as  the  fresh-w^ter  sands 
and  clays  of  the  Weald.  An  organic  limestone 
like  the  chalk  formed  in  the  open  ocean,  necessi- 
tates shores  where  sediments  were  laid  down. 


52  THE   STORY   OF  THE   EARTH. 

And  beyond  those  shores  of  the  chalk  sea  were 
land  surfaces  of  islands  and  continents  on  which 
plants  and  animals  survived  from  age  to  age. 

Lands  have  never  ceased  to  exist  from  the 
earliest  ages.  They  have  changed  their  forms. 
Their  height  of  elevation  above  the  sea  has  been 
altered  ;  they  have  been  broken  up  into  islands 
and  re-united  with  other  islands  newly  formed. 
The  lands  which  exist  at  the  present  day  are  built 
up  almost  entirely  of  water-formed  rocks,  which 
have  been  spread  out  one  upon  another  in  the 
ocean.  Every  continent  shows  this  history :  a 
succession  of  ancient  sea-beds,  with  the  deposits 
formed  upon  them,  alternating  occasionally  with 
old  land  surfaces  which  make  known  epochs  when 
the  sea-bed  emerged  from  the  ocean,  and  became 
land  as  it  is  now. 

The  shores,  with  their  pebble  beds  and  other 
evidences  of  tidal  movement  of  the  waters,  have 
persisted  from  the  earliest  times,  changing  their 
positions  upon  the  globe,  as  the  lands  altered 
their  forms,  never  entirely  passing  away  through 
the  long  epochs  of  geological  time,  although  they 
only  occasionally  come  back  again  to  the  places 
in  which  shores  had  previously  existed. 

The  open  ocean  with  its  limestones  has  proba- 
bly been  equally  persistent  and  as  variable  in  form. 
Very  little  is  known  of  limestones  which  may  have 
existed  in  the  earliest  geological  ages.  But  from 
their  thickness  and  importance  in  the  time  named 
Devonian  and  Carboniferous,  and  in  all  subse- 
quent times,  it  is  inferred  that  the  open  ocean  has 
persisted,  Chough  its  depth  has  varied.  There 
can  have  been  no  breaks  in  geological  time, 
though  there  are  breaks  in  the  continuity  of  land 
surfaces,  in  the  continuity  of  shore  lines,  and  the 


THE  SUCCESSION  OF  STRATA.  53 

continuity  of  deposits  of  the  open  sea.  These 
breaks  are  local,  like  the  breaks  which  are  made 
by  the  islands  or  lands  which  divide  the  sea,  and 
by  the  waters  which  separate  lands  from  each 
other. 

The  Succession  of  super -ijnposed  Rocks. 

A  sediment  may  be  followed  round  a  shore 
line,  so  that  it  has  everywhere  the  same  general 
character,  except  in  so  far  as  the  rocks  of  the 
cliffs  vary,  which  give  rise  to  pebble  beds  in  some 
localities  and  scarcely  any  sandy  particles  on  the 
shore  in  others.  As  a  rule,  tidal  work  sorts  and 
sifts  the  products  which  the  sea  carries  down  to 
its  depths,  so  that  they  are  arranged  in  bands 
which  are  parallel  to  the  coast.  The  particles 
vary  in  size  in-those  zones  of  deposit.  The  finer 
particles  remain  suspended  longest;  and  are  there- 
fore transported  to  the  greatest  distance  by  the 
moving  water.  Thus  there  is  a  horizontal  succes- 
sion of  rocks  on  successive  parts  of  the  same 
ocean  floor,  which  may  be  roughly  classed  as 
sands,  clays,  and  limestones.  Sands  formed  near- 
est to  shore  sometimes  pass  into  grits  and  pebble- 
beds.  And  the  limestones,  like  the  sands/ some- 
times alternate  with  clays  in  vertical  succession, 
where  they  pass  horizontally  into  each  other.  In- 
stances may  occur  where  limestones  extend  con- 
tinuously from  the  shore  to  the  open  ocean,  with- 
out intervening  deposits. 

The  horizontal  sequence  of  water-formed 
rocks,  observed  at  the  present  day,  explains  the 
meaning  of  the  vertical  succession  of  the  layers 
of  rock  termed  strata,  which  differ  from  each 
other  in  mineral  character.  By  their  superposi- 
tion they  build  up  most  of  the  visible  land,  as  well 


54  THE  STORY  OF  THE  EARTH. 

as  of  those  parts  which  are  hidden  under  the  oceans. 
Their  vertical  succession  depends  upon  successive 
changes  in  position  of  the  area  from  which  sedi- 
ments are  brought  into  the  sea. 

If  the  land  sinks  down  so  that  it  becomes 
smaller,  and  its  shores  recede,  each  kind  of  sedi- 
ment derived  from  it,  being  carried  by  the  moving 
water  the  same  distance  as  before  its  depression, 
is  transported  for  a  less  distance  out  to  sea  as 
compared  with  the  .deposit  formed  previously. 
Therefore  the  finer  sediments  on  a  sinking  sea- 
bed rest  upon  the  coarser  sediments,  which  had 
been  formed  previously,  when  the  source  of  sup- 
ply was  nearer  to  the  place  of  deposition.  In 
other  words,  clays  rest  upon  sands ;  while  the  new 
sands  rest  upon  areas  which  had  previously  been 
dry  land.  If  this  process  of  depression  continues, 
then  while  the  clays  follow  the  new  sands,  and 
become  super-imposed  upon  them,  limestones  are 
super-imposed  upon  clays. 

Sandstones  occasionally  give  evidence  that 
they  were  deposited  between  tide  marks,  in  pre- 
serving the  footprints  of  animals,  as  well  as  in 
the  ripple  marks,  sun-cracks  and  rain-prints  which 
were  formed  when  the  surfaces  dried  between  suc- 
cessive tides.  Such  memorials  are  preserved  in 
the  Trias  Sandstone  of  Cheshire,  and  the  Hast- 
ings Sand.  Clays  occasionally,  in  the  abundant 
remains  of  terrestrial  plants  which  they  yield, 
give  evidence  of  estnarine  origin,  which  may  not 
be  strictly  comparable  to  the  succession  of  con- 
ditions seen  upon  a  land  which  is  being  sub- 
merged. 

On  the  other  hand  some  deposits  are  formed 
upon  shores  which  are  rising,  and  advance  at  the 
expense  of  the  sea,  and  then  the  deposits  which 


THE  SUCCESSION   OF  STRATA.  55 

result  from  waste  of  the  land,  succeed  each  other 
vertically  in  reverse  order.  In  the  sea  which 
borders  the  coast  of  South  America,  the  sand  de- 
rived from  its  cliffs  may  be  carried  out  to  a  dis- 
tance of  from  20  to  150*  miles  from  the  shore. 
The  mud  formed  at  the  same  time  would  be  car- 
ried much  further.  If  then  such  a  land  were  to 
be  enlarged  by  slow  upheaval,  so  that  the  shore 
extended  over  the  area  which  had  previously  been 
the  shallow  sea,  two  sediments  which  would  still 
be  formed  would  be  carried  as  great  a  distance  as 
they  were  carried  previously,  and  the  sand  at  its 
furthest  limit  from  the  shore  would  gradually  ex- 
tend beyond  the  limit  of  the  sand  beneath  it,  and 
would  thus  be  super-imposed  in  part  at  least  upon 
clay.  In  like  manner  the  mud  sediment  would 
be  carried  further  than  the  mud  had  gone  pre- 
viously, so  that  it  would  similarly  rest  upon  lime- 
stone. 

Therefore,  under  the  influence  of  continual 
depression,  the  geological  deposits  come  to  be 
accumulated  in  the  vertical  order  of  sand,  clay 
and  limestone,  in  the  same  place.  While  under 
the  influence  of  continued  upheaval  the  vertical 
succession  comes  to  be  limestone,  clay,  sandstone. 

There  are  constant  oscillations  of  level  of 
land  which  are  evidenced  by  successions  of  sand 
and  clay,  or  limestone  and  clay,  which  are  local. 
And  occasionally  a  sediment  is  derived  simul- 
taneously from  two  different  sources,  as  when 
ancient  cliffs  furnish  sand,  and  an  ancient  river 
supplies  mud  which  is  deposited  at  the  same  time, 
over  part  of  the  same  area. 

The  layers  of  water-formed  rock  which  form 
every  land,  succeed  each  other  vertically  in  some 
such  order  as  sand,  clay  limestone,  limestone,  clay 


56  THE  STORY  OF  THE   EARTH. 

sand.  Their  order  in  Nature,  as  seen  in  the  cliffs 
and  on  the  surface  of  the  land,  is  evidence  of 
great  upward  and  downward  movements  both  of 
the  floor  of  the  ocean  and  the  dry  land,  which 
have  been  brought  about  by  foldings  of  the  rocks. 
Usually  these  rocks,  the  strata  of  sand  clay 
and  limestone,  rest  evenly  upon  each  other,  for 
the  upward  and  downward  movements  are  com- 
monly so  gradual,  that  while  the  rocks  are  dis- 
tinguished from  each  other  by  mineral  character, 
and  the  planes  of  bedding,  which  change  with 


FIG.  8.— Geological  map  of  part  of  Yorkshire,  showing  the  west- 
ward extension  from  Flamboro'  Head  of  the  Chalk  and  Hun- 
stanton  Limestone,  so  as  to  rest  unconformably  upon  the 
Kimeridge  Clay,  Lower  Oolites  and  Lias. 

depth  of  the  sea-bed,  there  is  no  physical  break 
in  the  succession  of  limestone  on  clay  or  clay  on 
sand,  and  the  beds  in  parallel  planes  of  deposit, 


THE   SUCCESSION   OF   STRATA.  57 

are  said  to  be  conformable  to  each  other.  This  is 
particularly  true  of  an  area  undergoing  depres- 
sion. Yet  as  depression  extends,  and  an  area 
which  had  previously  been  dry  land  is  submerged 
so  as  to  be  covered  with  new  deposits,  worn  from 
the  higher  land  which  is  near  to  the  now  sub- 
merged area,  such  a  new  layer  begins  a  new  order 
of  succession  in  that  district,  and  rests  upon  the 
edges  of  many  older  deposits  which  had  been 
tilted  up  and  worn  level,  so  that  their  edges  be- 
came exposed  before  the  old  land  was  raised  from 
the  sea.  Such  a  succession  is  said  to  be  uncon- 
formable.  There  is  an  unrepresented  interval  of 
time  between  such  unconformable  strata  and  the 
layers  on  which  they  rest;  but  the  unconformity 
is  local,  and  does  not  imply  any  real  break  in  the 
succession  of  rocks,  for  the  break  is  a  conse- 
quence of  the  submergence  of  the  denuded  land, 
which  had  interrupted  the  even  spread  of  sedi- 
ments by  the  water,  so  long  as  it  remained  above 
the  sea. 

On  the  other  hand,  when  land  is  undergoing 
upheaval,  and  the  shore  deposits  begin  to  be 
raised  out  of  the  water,  it  must  happen  that  the 
newest  formed  deposits  will  be  worn  up  and  re- 
mov,ed  before  they  emerge  from  the  sea.  There 
is  a  break  formed  in  this  way  in  the  horizontal 
sequence,  though  there  is  no  break  in  the  vertical 
sequence  of  strata.  Traced  by  their  mineral 
character  to  the  circumstances  in  which  they 
originate,  the  whole  succession  of  water-formed 
rocks  which  is  known  demonstrates  no  more  than 
three  or  four  great  oscillations  in  level  of  the 
earth's  surface,  which  have  converted  lands  into 
seas,  and  seas  into  lands. 

It  is  obvious  that  land  is  disturbed  in  level  in 


58  THE  STORY  OF  THE  EARTH. 

some  localities,  while  the  level  elsewhere  is  un- 
affected, so  that  the  succession  of  rocks  may  vary 
in  mineral  character  in  the  disturbed  district, 
with  no  indication  of  change  in  the  succession 
elsewhere.  On  this  account,  the  history  of  every 
part  of  the  earth  needs  to  be  told  separately  from 
the  other  parts,  for  too  little  is  yet  known  of  the 
detailed  events  which  took  place  in  the  successive 
periods  of  time,  in  the  different  portions  of  the 
globe,  to  piece  the  parts  of  the  story  together 
into  a  complete  history  of  the  earth. 


CHAPTER   VII. 

ORIGIN    OF    STRATIGRAPHICAL    GEOLOGY. 

GEOLOGY  originated  in  observation  of  the 
earth's  surface,  by  which  records  were  made  of 
the  order  and  arrangement  in  which  different 
rocks  occur  in  England  and  Wales.  This  knowl- 
edge is  expressed  in  two  laws.  The  first  is  the 
law  of  stratification.  It  affirms  that  the  rocks 
which  are  anywhere  exposed  on  the  surface  of 
the  country  are  usually  portions  of  layers,  which 
rest  successively  upon  each  other.  ThereTore 
they  rise  from  beneath  each  other,  in  the  order 
of  their  relative  antiquity,  whenever  they  are  in- 
clined to  the  plane  of  the  horizon.  Every  such 
layer  is  a  stratum.  Strata  differ  from  each  other 
in  relative  antiquity,  in  their  mineral  materials, 
thickness,  extension,  and  degree  of  disturbance 
from  the  original  condition  of  their  horizontal 
deposition.  The  law  of  succession  of  the  layers 
upon  each  other  is  named  their  superposition. 


ORIGIN   OF  STRATIGRAPHICAL  GEOLOGY.       59 

The  second  law  is  that  every  stratum  may  be 
identified  by  means  of  the  included  remains  of 
plants  and  animals,  termed  fossils,  which  lived 
when  its  rock  material  was  being  accumulated  in 
the  parUof  the  earth  in  which  it  is  found.  By 
these  fossils  the  exposed  edge  of  every  stratum 
may  be  traced  as  it  extends  through  the  country. 
Therefore  the  area  occupied  upon  the  surface  of 
the  country  by  each  geological  deposit  may  be 
drawn  upon  a  map.  A  map  made  in  this  way, 
which  defines  the  limits  of  strata,  lava  flows, 
crystalline  and  other  rocks  which  form  the  coun- 
try, is  a  Geological  map.  It  shows  how  the  strata 
in  a  country  may  be  distinguished  and  classified 
by  the  succession  of  groups  of  animals  and  plants 
which  have  followed  each  other  in  occupying  the 
same  portion  of  the  Earth's  surface. 

These  laws  were  discovered  about  1790  by 
William  Smith.  He  applied  them  in  travelling 
through  the  country,  so  as  to  make  the  first  Geo- 
logical Map  of  England  and  Wales,  which  was 
completed  in  1815.  In  1816  his  collection  of 
fossils,  which  distinguish  and  identify  the  several 
British  Strata,  was  placed  in  the  British  Museum. 
It  became  the  foundation  of  the  National^  Geo- 
logical Collection  and  the  beginning  of  all  Geo- 
logical Museums. 

Other  observers  had  recorded  the  order  of  the 
strata  in  different  localities,  and  in  some  cases 
had  recorded  the  occurrence  of  fossils  in  a  single 
stratum ;  but  without  making  the  discovery  that 
the  strata  may  be  identified  by  their  organic  re- 
mains. 

Dr.  Lister,  in  1684,  proposed  to  the  Royal 
Society  to  make  a  map  of  the  soils  in  our  coun- 
try. This  was  the  first  proposal  to  make  a  Geo- 


60  THE  STORY  OF  THE   EARTH. 

logical  Map.  In  one  of  his  writings  Dr.  Lister 
gives  a  drawing  of  a  small  fossil,  a  Belemnite, 
and  states  correctly,  that  it  is  found  in  all  the 
cliffs  along  the  Yorkshire  wolds,  for  a  distance  of 
more  than  100  miles,  by  Speeton,  Londesbro'  and 
Caistor,  but  always  in  a  red  ferruginous  earth 
[now  known  as  the  Hunstanton  Limestone]. 

Mr.  John  Strachey  in  1719  laid  before  the 
Royal  Society  evidence  that  the  upturned  and 
levelled  edges  of  the  Coal  Strata  in  the  Somerset- 
shire Coal  Basin  were  covered  by  nearly  hori- 
zontal beds  of  the  Red  Marl,  Lias,  and  Oolite. 

The  Rev.  John  Holloway  in  1723  described  to 
the  Royal  Society  the  parallelism  of  the  Chalk 
of  the  Gog-Magog  and  Chiltern  Hills,  the  Sand 
Hills  of  Woburn,  and  the  Clay  country  drained 
by  the  Cam,  Ouse,  Nen,  and  Isis. 

The  Rev.  John  Mitchell  in  1760  stated  to  the 
Royal  Society  that  "  we  ought  to  meet  with  the 
same  kinds  of  earths,  stones  and  minerals  appear- 
ing at  the  surface  in  long  narrow  strips,  and  lying 
parallel  to  the  greatest  rise  of  any  long  ridges  of 
mountains,  and  in  fact  we  find  them  [thus  ex- 
posed]." The  ridge  in  England  which  influences 
the  direction  of  the  strata  is  said  to  run  first 
north  to  south,  and  then  from  north-east  to 
south-west.  Travelling  between  the  Chalk  hills 
of  Cambridgeshire  and  the  Coal  of  Nottingham 
and  Yorkshire,  he  observed  the  succession  of  the 
strata;  and  in  1788,  gave  to  Smeaton  the  Engi- 
neer, a  table  of  these  strata,  with  their  thick- 
nesses. They  are  enumerated  in  vertical  se- 
quence as  Chalk,  Golt,  Sand  of  Bedfordshire, 
Northampton  lime  and  Portland  lime  in  several 
strata,  Lyas,  Sand  of  Newark,  Red  Clay  of  Tux- 
ford,  etc.,  Sherwood  Forest  pebbles  and  gravel 


ORIGIN   OF   STRATIGRAPHICAL  GEOLOGY.       6 1 

[fine  white  sand],  Roche  Abbey  and  Brotherton 
limes,  Coal  Strata  of  Yorkshire.  This  table  was 
given  to,.Henry  Cavendish,  who  preserved  it. 

Mr.  John  Whitehurst  in  1778  gave  an  account 
of  the  Geological  structure  of  Derbyshire ;  and 
remarks :  the  strata  follow  each  other  in  a  regu- 
lar succession,  both  as  to  thickness  and  quality, 
insomuch  that  by  knowing  the  incumbent  stra- 
tum, together  with  the  arrangement  thereof  in 
any  particular  part  of  the  earth,  we  come  to  a 
perfect  knowledge  of  all  the  inferior  beds,  so  far 
as  they  have  been  previously  discovered  in  the 
adjacent  country. 

Smeaton  in  1786  expressed  his  belief  that  the 
Lias  extends  from  Watchet  in  Somersetshire  to 
Barrow  in  Leicestershire,  probably  with  few 
breaks  in  continuity,  and  through  the  vale  of 
Belvoir  into  Nottinghamshire  and  Lincolnshire, 
beyond  Grantham  and  Long  Bennington. 

There  is  no  reason  to  believe  that  William 
Smith  had  heard  of  any  of  these  observations. 
He  was  born  23rd  March  1769,  at  Churchhill  in 
/Oxfordshire,  upon  the  Oolites.  He  became  a 
/land  surveyor  and  engineer;  and  at  the  age  of 
twenty-one  had  found  out  for  himself  the  succes- 
sion of  such  rocks  as  he  had  seen,  and  had  begun 
to  compare  the  appearances  at  one  locality  with 
those  observed  at  a  distance.  His  work  was  dis- 
tinguished from  that  of  all  predecessors  by  his 
method  of  untiring  persistence  in  observing  facts 
of  stratification  ;  activity  in  comparing,  extending 
and  establishing  the  conclusions  to  which  those 
observations  led ;  and  care  in  recording  upon  his 
map  nothing  but  what  he  had  seen  and  proved. 
This  work  caused  him  to  be  known  through  the 
country  as  Strata  Smith ;  recognised  among  geol- 


62  THE   STORY  OF   THE   EARTH. 

ogists  as  the  Father  of  Geology  ;  and  honoured  as 
a  great  original  discoverer  in  science. 


CHAPTER  VIII. 

FOSSILS. 

Geological  and  Zoological  Aspects  of  Fossil  Plants 
and  Animals. 

IN  the  early  days  of  geology  fossils  were  re- 
garded with  interest  because  some  species  were 
limited  in  their  range  in  time  and  only  found  in 
certain  rocks.  Attention  was  given  chiefly  to 
extinct  species  which  were  most  abundant  in  each 
of  the  geological  deposits.  A  large  amount  of 
practical  work,  in  mapping  the  distribution  of  the 
strata,  was  done  with  the  aid  of  very  slight  knowl- 
edge of  a  few  species  of  animals. 

It  became  possible  also  to  group  the  rocks  to- 
gether in  a  rough  way  by  limitation  to  the  vertical 
range  of  a  few  fossils.  The  oldest  rocks  were 
defined  as  those  containing  Trilobites;  the  mid- 
dle group  as  those  containing  Ammonites;  and 
the  newest  group  as  containing  Nummulites.  The 
geologist,  having  to  classify  the  rocks  and  iden- 
tify them,  was  influenced  in  making  divisions  of 
the  strata  occur  wherever  a  difference  in  life  of 
any  kind  would  permit  the  separation  of  strata,  or 
groups  of  strata,  from  each  other. 

A  dim  idea  prevailed  that  the  change  in  life 
was  in  some  way  connected  with  the  succession 
of  geological  periods  of  time.  Hypotheses  were 
put  forward  that  the  groups  of  strata  correspond 


FOSSILS.  63 

to  about  six  successive  epochs,  during  which  the 
life  gradually  became  higher  in  the  details  of  its 
organization.  This  theory  was  not  suggested  by 
examination  of  the  rocks  and  their  contents,  be- 
cause divisions  which  separate  strata  in  Europe 
are  differently  placed  in  America.  The  hypothe- 
sis endeavoured  to  forestall  results  at  which 
science  might  arrive.  The  species  of  fossils 
found  in  each  stratum  were  supposed  to  have 
been  created  in  the  period  of  time  when  they 
were  first  met  with ;  and  to  have  become  extinct 
when  they  disappeared  with  the  succession  of 
newer  strata. 

Naturalists  found  that  existing  life  varies  with 
elevation  above  the  sea  level,  and  that  there  is  a 
relation  between  distribution  in  height  and  in 
horizontal  area.  While  some  of  the  plants  found 
in  Great  Britain  are  identical  with  those  of  Ger- 
many, there  are  a  few,  living  on  high  ground, 
which  are  Scandinavian  types.  In  the  south-west 
of  Ireland  there  are  a  few  Spanish  and  Portuguese 
types.  The  Scandinavian  life  was  accounted  for 
on  the  hypothesis  that,  in  a  recent  period  of  geo- 
logical time,  those  plants  spread  over  land  which 
is  now  the  North  Sea,  when  the  temperature  was 
lower  than  it  is  now.  When  the  German  types  of 
plants  subsequently  spread  over  England,  the 
Scandinavian  species,  which  could  endure  greater 
cold,  survived  upon  the  hills;  much  as  the  Celtic 
population  may  have  receded  to  the  high  ground 
before  the  invading  Saxon  peoples. 

Considerations  of  this  kind  indicate  two  great 
laws.  First,  that  the  existing  life  which  occupies 
the  earth's  surface  is  grouped  in  series  of  geo- 
graphical assemblages,  each  of  which  may  be 
termed  a  life  province ;  and  secondly,  that  these 


64  THE   STORY  OF  THE   EARTH. 

provinces  occupy  changed  areas  of  the  earth's 
surface,  with  alterations  in  the  level  of  land. 

In  the  same  way  it  was  found  that  life  in  the 
sea  varies  with  the  depth  of  the  water.  Sea-shells 
which  live  between  tide-marks,  and  are  adapted 
to  exist  more  or  less  exposed  in  atmospheric  air, 
are  different  in  genera  or  species  to  those  in  the 
deeper  water,  where  the  great  growths  of  sea 
plants  are  found.  Marine  life  again  changes  its 
character  with  greater  depth.  The  shells  which 
would  be  indicative  of  a  shore,  travel  along  the 
shore ;  and  the  shells  which  are  found  in  clays, 
are  rarely  met  with  in  sand.  Marine  life  also 
varies  geographically  in  the  horizontal  direction, 
because  there  are  natural  history  provinces  of  life 
in  the  sea,  which  may  also  change  their  area, 
when  the  depth  of  water  changes,  so  as  to  scatter 
or  concentrate  or  combine  the  life. 

About  the  year  1864  it  began  to  be  urged  that 
the  differences  found  in  the  fossil  life  between 
two  successive  geological  deposits,  were  not  due 
to  great  denudations  of  intervening  strata,  which 
had  removed  the  intervening  transitional  organ- 
isms, making  breaks  in  the  geological  record,  but 
were  the  results  of  geographical  migrations  of 
organisms,  so  that  these  animals  and  plants  came 
into  an  area  which  they  had  not  previously  occu- 
pied, by  moving  away  from  one  which  had  for- 
merly been  their  home.  When  fossilized,  the 
remains  of  such  a  group  indicate  a  different  as- 
semblage of  animals  or  plants  to  those  which 
lived  previously  in  the  area,  when  the  life  in  the 
underlying  stratum  accumulated  and  was  fossilized 
in  the  same  way. 

Thus  it  is  intelligible  that  the  distribution  of 
life  in  the  strata  has  been  brought  about  in  the 


FOSSILS.  65 

same  way  as  the  distribution  of  life  is  varied 
upon  the  earth's  surface  now.  And  instead  of 
fossils  in  geological  formations  representing  a 
multitude  of  successive  creations,  there  appears 
to  be  but  one  creation.  These  types  of  life  sur- 
vived from  the  earliest  time  by  undergoing  more 
or  less  adaptation  to  altered  conditions,  as  a 
necessary  circumstance  for  their  perpetuation 
through  all  the  revolutions  which  the  earth's  sur- 
face has  undergone. 

Thus  it  is  known  that  the  elephant,  hippo- 
potamus, lion,  hyaena,  rhinoceros,  which  are  now 
living  in  Africa,  have  been  common  animals  in 
Europe  and  Britain  since  the  time  during  which 
men  have  lived  here ;  that  those  animals  have 
changed  their  habitation ;  and  that  the  area  of 
the  life  province  to  which  they  belong  is  mani- 
festly altered.  There  are  no  animals  more  dis- 
tinctive of  Africa  at  the  present  day  than  the 
hippopotamus  and  ostrich,  but  in  a  recent  ter- 
tiary period  of  geological  time,  these  animals  left 
their  remains  in  rocks  of  Northern  India,  in  asso- 
ciation with  extinct  allies  of  the  giraffe,  a  type 
which  is  now  limited  to  Africa.  And  so  another 
change  in  the  area  occupied  by  a  natural  history 
province  of  life  is  made  known  by  remains  of 
animals  preserved  in  the  rocks. 

All  down  the  sequence  of  the  geological  ages 
the  story  is  of  the  same  kind.  Wherever  there 
is  a  change  in  the  material  of  which  rocks  are 
formed  there  is  a  change  in  the  distribution  of 
life  on  the  earth.  The  upheaval  or  depression 
which  varies  the  distribution  of  the  mineral  mat- 
ter and  produces  the  succession  of  strata  is  also 
the  cause  which  varies  the  distribution  of  life. 
Therefore  the  fossils  found  in  any  geological 


66        THE  STORY  OF  THE  EARTH. 

formation  are  a  portion  of  a  natural  history 
province,  which  has  been  preserved  in  the  condi- 
tion in  which  it  existed  on  the  earth's  surface  at 
that  particular  epoch  of  time. 

If  we  suppose  land  and  sea  at  the  present 
day  to  be  occupied  over  their  areas  with  natural 
history  provinces  of  life,  in  the  manner  in  which 
they  have  been  marked  out  by  naturalists,  such 
provinces  are  manifestly  the  survival  of  the  life 
which  has  existed  in  the  several  periods  of  the 
geological  record.  They  have  reached  their 
present  positions  in  consequence  of  the  geolog- 
ical circumstances  of  rock  folding  in  the  earth's 
crust  which  have  given  the  earth's  surface  its 
present  form.  This  truth  is  the  only  explanation 
of  the  succession  of  life  in  the  past  ages  of  the 
earth's  history.  It  is  impossible  to  imagine  any 
change  in  life  between  the  oldest  deposit  known 
and  the  bed  which  succeeded  it,  unless  the  life 
was  already  different  in  an  adjacent  area  of  the 
ocean,  so  that  a  new  natural  history  province 
could  be  superimposed  upon  that  which  had  pre- 
viously occupied  the  ground.  The  fossils  of  the 
geological  formations  are  therefore  the  records  of 
the  succession  of  the  natural  history  provinces  of 
life  on  the  earth.  Each  province  has  been  formed 
by  geological  changes.  They  have  succeeded 
each  other  like  the  movements  of  chess-men  upon 
the  same  square  of  the  chess-board.  In  this  pro- 
cess many  of  the  old  life  provinces  are  broken 
up,  and  their  constituent  animals  and  plants  scat- 
tered and  intermixed  with  others,  almost  beyond 
recognition.  Such  survivals  have  not  been  accom- 
plished, however,  without  the  earth  losing  many 
of  the  kinds  of  life  with  which  the  geological  story 
begins,  and  which  characterize  its  greater  epochs. 


FOSSILS.  67 

The  Succession  of  Life. 

The  oldest  geological  deposits  in  the  Cam- 
brian period  give  no  indication  of  a  commence- 
ment of  life  on  the  earth.  The  assemblage  of 
fossils,  after  eliminating  the  types  which  have  be- 
come extinct,  is  comparable  to  such  as  might  be 
found  upon  an  existing  sea-bed.  The  most  an- 
cient groups  of  fossils  in  the  stratified  rocks  lend 
no  support  to  the  hypothesis  that  they  are  stages 
of  a  process  by  which  animals  came  successively 
into  existence,  in  the  order  of  their  grades  of 
organisation.  There  are  already  several  groups 
of  animals  co-existing,  associated  with  each  other 
as  they  are  upon  an  existing  sea-bed.  On  many 
shores  at  the  present  day  the  variety  in  life  is  not 
greater  than  the  geologist  finds  in  a  quarry  or 
cliff  after  examining  a  few  yards  of  rock. 

Each  of  the  great  divisions  of  the  animal  king- 
dom has  representatives  in  very  old  rocks.  Man 
is  limited,  so  far  as  is  at  present  known,  to  the 
newest  deposits.  But  geological  research  has 
pushed  further  and  further  backward  in  time,  the 
epoch  in  which  each  of  the  highest  types — mam- 
mals, birds,  reptiles,  fishes — is  first  met  v;ith. 

Sometimes  the  earlier  rocks  are  fancifully 
spoken  of  as  the  age  of  fishes ;  those  of  the 
middle  period  are  named  the  age  of  reptiles ;  and 
the  latest  rocks  are  termed  the  age  of  mammals. 
Each  of  those  groups  of  animals  puts  on  a  con- 
siderable diversity  of  organisation  in  the  epochs 
which  it  is  supposed  to  characterize ;  and  each 
includes  some  extinct  groups  which  are  not  met 
with  at  the  present  day ;  or  subsequent  to  the 
epoch  which  the  group  characterizes.  On  the 
other  hand,  mammals  are  not  only  not  limited 


68  THE   STORY  OF  THE   EARTH. 

to  the  tertiary  strata,  but  have  been  recorded  as 
extending  to  the  Trias,  the  beginning  of  the 
secondary  rocks.  Indications  of  their  existence 
occur  in  connection  with  each  of  the  old  land 
surfaces  which  the  strata  make  known  in  the 
south  of  England.  Birds  have  been  found  on 
two  different  horizons  in  the  secondary  rocks. 
The  presence  in  those  secondary  rocks  of  animals 
so  remarkable  as  Ichthyosaurs,  Plesiosaurs,  Or- 
nithosaurs,  Dinosaurs,  and  Anomodonts,  fully 
justifies  the  term,  age  of  reptiles.  The  modern 
type  of  crocodiles,  lizards,  turtles,  and  snakes, 
which  are  the  true  reptiles  of  the  present  time, 
do  not  extend  back  to  very  early  parts  of  the 
secondary  epoch,  so  far  as  is  known  at  present. 
Extinct  groups  of  reptiles  such  as  the  Anomo- 
donts and  Labyrinthodonts  date  back  at  least  as 
far  as  the  time  in  which  the  Permian  and  Carbon- 
iferous coal  was  accumulated.  The  great  facts 
which  life  presents  to  us  when  examined  by  means 
of  fossil  remains,  preserved  in  the  succession  of 
strata,  are :  first,  that  it  has  been  always  changing 
in  the  same  locality,  in  the  same  way  as  a  fauna 
or  flora  undergoes  change  at  the  present  day.  In 
the  lifetime  of  individuals,  plants  and  insects  have 
disappeared  from  the  fen  district  of  Cambridge- 
shire under  the  influence  of  embanking  and  drain- 
ing, just  as  in  historic  times  animals  like  the  wolf, 
brown  bear,  beaver  and  roebuck,  have  disappeared 
from  South  Britain.  In  other  parts  of  the  world 
the  existing  fauna  has  become  poorer  by  the  ex- 
tinction of  birds  like  the  Dodo,  and  the  Moa. 
This  process  of  extinction  has  never  ceased.  Its 
evidences  remain  in  the  extinct  species  which 
characterize  every  geological  deposit. 

The  process  of   extinction    has   extended   to 


FOSSILS.  69 

some  larger  groups,  such  as  in  natural  history  are 
termed  Orders  of  Animals.  Thus  in  the  old  slaty 
rocks  termed  Cambrian  and  Silurian  the  entire 
group  of  animals  termed  Graptolites  is  extinct. 
In  the  primary  rocks  there  is  an  extinct  group  of 
corals,  termed  Rugosa,  which  have  the  radiating 
shelly  partitions  termed  septa,  in  multiples  of 
four.  There  are  small  extinct  groups  of  Echino- 
derms  in  the  silurian  and  carboniferous  rocks, 
allied  to  the  sea  urchins,  named  Cystoidea  and 
Blastoidea.  Among  Crustacea  there  are  the  ex- 
tinct groups  Trilobites,  comprising  more  than 
fifty  genera  ;  and  the  Merostomata,  comprising 
animals  which  are  allied  to  the  king  crabs  and 
scorpions. 

Other  groups  of  animals,  though  not  entirely 
extinct,  are  much  better  represented  in  the  fossil 
state  than  in  existing  nature.  Most  of  the  genera 
of  the  groups  of  lamp-shells  named  Brachiopoda, 
are  extinct,  and  found  only  in  the  Primary  rocks; 
and  the  larger  number  of  allies  of  the  Nautilus 
are  found  in  a  fossil  state,  partly  in  the  primary, 
and  partly  in  the  secondary  period  of  time. 

A  number  of  the  existing  groups  of  animals 
date  from  very  remote,  if  not  from  the,  earliest 
known  geological  ages.  The  genera  in  which 
they  are  first  met  with,  frequently  appear  to  have 
persisted  ever  since,  without  undergoing  any  ap- 
preciable change,  beyond  those  minor  modifica- 
tions which  distinguish  species.  Although  the 
fruits  of  the  Araucaria,  of  various  pines,  and  of 
Pandanus,  are  found  in  the  lower  Secondary  rocks, 
it  is  not  until  the  latter  part  of  the  secondary 
period  that  any  deposit  yields  enough  fossil  leaves 
to  enable  the  vegetation  of  the  earth  to  be  com- 
pared as  a  group  with  living  types.  The  common 


70  THE   STORY  OF    THE   EARTH. 

genera  of  ferns  of  the  present  day  are  well  repre- 
sented in  strata  older  than  the  chalk,  by  such 
types  as  Pteris,  Asplenium,  Adiantum,  Aspidium, 
and  Gleichenia.  Palms  are  represented  by  Nipa. 
There  are  numerous  representations  of  the  oak, 
willow,  beech,  fig,  laurel,  ebony,  magnolia.  Noth- 
ing is  known  of  the  origin  of  this  ancient  cretace- 
ous flora,  but  there  is  no  ground  for  believing 
that  it  suddenly  came  into  existence  in  widely 
separated  parts  of  the  world,  where  it  is  first  met 
with. 

In  the  oldest  group  of  rocks  every  class  of 
animals  is  represented  by  many  genera  which 
.still  live.  Thus  the  Foraminifera,  which  fill  so 
large  a  place  in  the  life  of  the  open  ocean  at  the 
present  day,  are  represented  in  the  Silurian  period 
by  the  genera  Dentalina,  Lagena,  Nodosaria,  Tex- 
tularia. 

The  existing  genera  of  Echinoderms  are  not 
known  from  so  early  a  period  ;  but  in  the  begin- 
ning of  the  secondary  time  Cidaris  and  many 
other  genera  are  found,  which  abound  at  the  pres- 
ent day. 

Among  shells  the  Brachiopods  Lingula  and 
Crania,  Discina,  Rhynconella,  Terebratula  and  oth- 
ers survive  from  the  older  primary  time. 

The  common  bivalve  shells,  which  have  few 
representatives  in  the  Primary  rocks,  include  such 
familiar  forms  as  Pecten,  Pinna,  Cardiun,  Area, 
Avicula. 

The  common  Univalve  shells  begin  with  such 
forms  as  Patella,  Pleurotomaria,  Chiton,  Natica, 
Trochus,  Dentalium,  which  have  never  since  been 
absent  from  the  earth.  The  Nautilus  dates  from 
a  very  early  period. 

Thus,  although  the  history  of  life  has  left  be- 


FOSSILS.  71 

hind  enough  extinct  entombed  forms  to  enable 
every  deposit  to  be  recognised  by  their  remains, 
the  great  lesson  of  fossil  remains  is  not  so  much 
extinction,  as  survival  and  persistence  upon  the 
earth  of  the  life  which  has  once  existed.  The 
natural  inference  would  be  that  the  variety  in 
kinds  of  life  has  been  steadily  diminishing  from 
the  earliest  time,  owing  to  the  loss  of  the  extinct 
groups  of  plants  and  animals.  But  with  each 
group  of  newer  strata,  genera  and  families  of 
animals  are  met  with  among  the  fossils,  which 
were  not  known  in  the  older  sets  of  fossils. 
There  is  perhaps  no  proof  that  they  were  pre- 
viously absent  from  the  earth  ;  and  it  is  possible 
that  some  of  them  may  have  come  into  existence 
as  modifications  of  the  types  which  were  already 
in  existence. 

The  variation  which  life  undergoes  as  the 
condition  of  its  existence. 

There  is  a  principle  which  affects  the  history 
of  life,  which  necessitates  that  new  modifications 
of  plants  and  animals  should  constantly  come  into 
existence,  under  the  varying  conditions  whiph  the 
earth's  surface  assumes.  The  different  organic 
types  are  saved  from  extinction  by  manifesting 
some  degree  of  adaptation  to  altered  circum- 
stances. It  is  this  property  which  enables  the 
genus  to  survive  from  the  earliest  times.  It 
undergoes  a  series  of  changes  by  which  'slight 
differences  of  form  or  ornament  are  perpetuated 
for  a  time,  eventually  giving  place  to  another 
similar  series  of  modifications;  and  these  char- 
acters distinguish  the  species  of  which  the  genus 
consists.  Even  persons  who  are  not  trained  to 


72  THE   STORY  OF  THE   EARTH. 

recognise  the  technical  characters  by  which  ani- 
mals and  plants  are  classified,  are  aware  that 
there  are  different  kinds  of  scallop  shells,  and 
different  kinds  of  cockles.  The  change  in  form 
and  ornament  can  often  be  seen  to  originate  as  a 
consequence  of  the  home  of  the  shells  being  a 
place  where  the  water  is  still,  or  one  where  it  is 
exceptionally  disturbed,  the  ribs  of  shells  being 
always  stronger  in  rough  water.  The  presence 
of  fresh  water  in  an  estuary  would  appear  to  be 
a  frequent  cause  of  variation,  not  only  in  orna- 
ment, but  in  form.  Such  variations  tof  the  com- 
mon periwinkle  and  purple  shell  are  found  in 
Crag-beds  at  Norwich,  and  seen  in  inlets  on  the 
coast  at  the  present  day.  Many  of  these  varia- 
tions are  such  as  might  characterize  different 
genera  if  they  were  persistent  and  became  per- 
manent characters,  but  they  do  not  even  consti- 
tute species,  and  are  only  regarded  as  local  races 
due  to  local  causes.  If  it  were  possible  that  after 
a  local  race  had  come  into  existence,  another  set 
of  circumstances  affected  it  so  as  to  cause  varia- 
tion to  take  place  in  some  new  direction,  it  may 
be  that  what  was  previously  but  a  race  character, 
would  be  perpetuated  in  all  the  new  modifica- 
tions, and  become  the  distinctive  attribute  of  a 
species,  or  even  of  a  genus.  The  capacity  of  an 
animal  for  variation  is  usually  in  the  develop- 
ment of  something  new,  which  did  not  previ- 
ously exist ;  but  the  most  remarkable  evidences 
of  variation  are  in  the  loss  of  parts  which  had 
existed  in  animals  in  a  previous  period  of  time. 
The  capacity  for  variation  is  strikingly  seen  in 
the  manner  in  which  the  antlers  of  a  deer  become 
complicated  year  by  year,  by  the  development  of 
new  processes.  In  the  present  state  of  knowledge 


FOSSILS.  73 

certain  fossil  deer  appear  to  have  had  antlers 
which  were  less  complicated  ;  and  in  others  the 
antlers  were  more  complicated.  It  is  on  such 
characters  that  species  of  deer  are  distinguished. 

All  the  higher  forms  of  life  which  are  dis- 
tinguished in  classification,  are  records  of  loss. 
Thus  there  can  be  no  doubt  that  the  common 
horse  is  closely  related  to  the  fossil  horse  named 
Hipparion,  which  had  three  toes  on  each  foot,  and 
the  existing  horse  still  preserves  rudiments  of  the 
lateral  toes  which  have  been  lost,  in  the  splint 
bones,  which  occur  at  the  sides  of  each  cannon 
bone.  Attempts  have  been  made  to  show  that 
the  three-toed  horse  had  ancestors  with  five  toes, 
so  that  by  loss  of  the  digits  of  the  feet,  which  are 
consequences  of  the  ways  in  which  the  toes  are 
used,  genera  may  come  into  existence.  At  pres- 
ent there  is  very  little  in  the  way  of  fact  out  of 
which  such  a  history  could  be  constructed.  Sci- 
ence can  only  be  carried  on,  on  a  basis  of  un- 
broken evidence,  from  facts,  which  are  to  the 
scientific  man  what  capital  is  to  the  merchant. 
There  is,  however,  no  doubt  that  the  mammals 
have  lost  the  composite  structure  of  the  lower 
jaw,  which  is  found  in  reptiles ;  and  that  reptiles 
have  lost  the  greater  part  of  the  arch  of  bones 
which  in  fishes  intervenes  between  the  brain  case 
and  the  lower  jaw,  if  their  structures  are  inherited 
from  one  group  to  the  other. 


74  THE   STORY   OF   THE   EARTH. 

CHAPTER   IX. 

THE     CLASSIFICATION    OF    WATER-FORMED     ROCKS. 

IN  every  country  breaks  exist  in  the  con- 
tinuity of  the  strata.  Such  interruptions  in  se- 
quence are  in  progress  at  the  present  day  by  the 
upheaval  of  land  of  existing  islands,  and  conti- 
nents, which  intermits  the  deposition  of  marine 
strata.  Such  breaks  are  evidenced  by  want  of 
conformity  in  the  order  of  succession  of  the  de- 
posits. This  is  one  of  the  main  grounds  for  di- 
viding geological  deposits  from  each  other.  The 
breaks  which  exist  in  any  one  country  are  some- 
what limited  in  the  area  which  they  affect.  They 
can  never  be  world-wide  divisions  between  strata. 
Strata  are  also  divided  according  to  their  differ- 
ences in  predominant  mineral  character.  The 
changes  which  take  place  in  the  prevalent  types 
of  extinct  life  which  they  severally  preserve,  give 
grounds  for  division  of  deposits,  so  that  the  cessa- 
tion of  an  ancient  group  of  animals,  or  the  in- 
coming of  a  new  group,  makes  a  division  possible 
between  the  strata. 

There  is  no  necessary  connection  between  the 
break  in  stratification,  termed  unconformity,  and 
the  break  in  life.  Frequently  there  is  a  great 
change  in  fossils  between  two  successive  strata 
without  an  indication  of  unconformity.  It  is 
difficult  to  understand  how  the  life  can  change 
appreciably  without  a  change  in  the  level  of 
adjacent  land,  which  causes  the  life  of  an  adja- 
cent area  to  migrate.  An  unconformity  is  not  of 
necessity  any  greater  evidence  of  an  unrepre- 
sented interval  of  time  than  conformity ;  because 


CLASSIFICATION   OF  WATER-FORMED   ROCKS.      75 

the  unconformable  beds  might  always  be  traced 
to  a  district  where  they  become  conformable,  so 
that  there  is  no  break  in  the  geological  record. 

The  changes  in  life  between  conformable 
strata,  are  no  more  than  the  differences  which 
zones  of  life  assume  with  depth.  As  a  pebble 
bed  changes  to  a  sandstone,  its  life  alters  from 
the  fauna  of  the  littoral  zone  between  tide  marks, 
to  the  fauna  of  the  deeper  laminarian  zone.  As 
the  sand  is  succeeded  by  a  clay  the  fauna  alters 
to  the  life  of  the  coralline  zone.  Therefore  there 
is,  from  the  point  of  view  of  the  existing  distribu- 
tion of  plants  and  animals,  a  necessary  change  of 
life,  with  change  in  stratification,  which  has  no 
important  connection  with  imperfections  in  the 
geological  record. 

The  breaks  in  life  and  in  stratification  were 
stated  by  the  late  Sir  Andrew  Ramsay  in  the 
following  series:  Between  the  Lingula  flags  and 
the  overlying  Tremadoc  slates  there  is  a  nearly 
complete  break  in  genera  and  species ;  and  un- 
conformity is  probable.  There  is  the  same 
condition  between  the  Tremadoc  slates  and  the 
Arenig  rocks;  and  between  the  Bala  and  Caradoc 
beds  below,  and  the  lower  Llandovery  above. 
There  is  a  great  break  in  species  in  alf  these 
examples,  and  probably  unconformity  as  well, 
but  the  unconformity  is  not  seen.  Between  the 
Lower  Llandovery  and  Upper  Llandovery  beds 
a  break  in  life  occurs,  and  marked  unconformity ; 
and  between  the  Upper  Llandovery  beds  and 
Wenlock  beds,  is  similar  evidence  of  a  break  in 
succession.  The  Old  Red-sandstone  however 
shows  no  sign  of  unconformity  at  the  junction 
where  it  succeeds  the  Ludlow  rocks  at  the  top  of 
the  Silurian,  and  no  break  in  life  though  both 


76  THE   STORY  OF   THE   EARTH. 

might  be  expected.  Nor  does  any  break  occur 
be.tween  the  upper  limit  of  the  fresh  water  old 
red  sandstone  and  the  marine  carboniferous  rocks 
in  the  Welsh  country.  The  carboniferous  rocks 
are  usually  conformable  from  top  to  bottom;  but 
there  is  sometimes  an  unconformable  succession 
of  Millstone  grit  upon  mountain  limestone,  in  the 
Forest  of  Dean.  There  is  a  great  unconformity 
between  the  Carboniferous  rocks  and  the  Per- 
mian. This  makes  a  total  of  ten  physical  breaks 
which  are  evidenced  during  the  primary  portion 
of  geological  time. 

There  is  a  complete  stratigraphical  break,  or 
unconformity  between  the  Trias  and  the  Permian. 
Near  Ormskirk  the  new  Red  Marl  rests  uncon- 
formably  on  the  new  Red  Sandstone.  There  is 
no  visible  unconformity  between  the  Rhaetic  beds 
and  the  Lias,  which  rests  upon  them,  but  the 
change  in  life  indicates  a  great  break  in  the 
uniformity  of  previous  conditions.  There  is  no 
complete  unconformity  between  the  Lias  and  the 
overlying  Inferior  Oolite.  But  the  change  in  life 
to  this  deposit,  and  through  all  the  succeeding 
divisions  of  the  Oolites,  is  such  as  may  be  asso- 
ciated with  unconformity  in  adjacent  areas.  At 
the  top  of  the  Oolites  there  is  an  insensible  pas- 
sage from  the  marine  Portland  limestone  to  the 
Purbeck  beds.  But  since  the  Purbeck  deposits 
include  terrestrial  surfaces,  and  are  largely  of 
fresh-water  origin,  an  unconformity  must  exist 
in  the  south  of  England  in  this  part  of  the  suc- 
cession. The  wealden  beds  may  also  be  uncon- 
formable. But  in  the  overlying  cretaceous  series 
of  deposits,  the  apparent  unconformity  is  an 
overlap  on  the  older  strata  which  gave  increased 
geographical  extension  to  the  Hunstanton  lime- 


CLASSIFICATION   OF  WATER-FORMED   ROCKS.      77 

stone  and  Chalk  in  the  north,  in  Yorkshire;  and 
to  the  Greensand  and  Chalk  in  the  south-west  of 
England. 

There  is  no  other  physical  break  in  this  coun- 
try till  that  between  the  chalk  and  the  tertiary 
strata,  which  is  partly  bridged  in  Belgium,  and 
perhaps  entirely  bridged  over  in  North  America. 
The  upheaval  of  a  succession  of  land  surfaces  in 
the  tertiary  period  is  evidence  of  remarkable 
breaks  in  the  sequence  of  deposits,  and  then  a 
great  gap,  unrepresented  by  strata  in  England, 
occurs  in  the  middle  tertiary  period.  The  mani- 
fest physical  breaks  in  the  area  in  which  the  Brit- 
ish strata  were  deposited,  are  much  fewer  than 
the  breaks  in  the  succession  of  life,  many  of  which 
are  evidently  due  to  the  way  in  which  life  is  dis- 
tributed in  successive  zones  in  depth.  Therefore 
there  has  been  no  uniform  principle  in  distinguish- 
ing the  strata  from  each  other  by  their  fossils; 
and  more  attention  has  been  paid  to  the  differ- 
ences in  life,  than  to  the  circumstances  by  which 
the  differences  were  caused. 

In  England  the  principal  changes  in  marine 
life  occur  (i)  between  the  Silurian  and  Devonian 
rocks,  though  the  changes  in  types  of  life  appear 
to  be  unimportant. 

(2)  Between  the  Primary  and  Secondary  rocks 
there  is  a  great  change  in  both  the  marine  and 
terrestrial  life. 

(3)  Between  the  Oolites  and  Cretaceous  rocks 
there  is  apparently  an  important  change  in  the 
terrestrial  life,  though  the  change  in  the  marine 
life  is  less  marked. 

(4)  The  gap  in  the  marine  succession  between 
the  Secondary  and  Tertiary  is  very  striking;  but  the 
gap  in  the  terrestrial  plant  life  appears  to  be  small. 


78  THE   STORY   OF   THE   EARTH. 

It  is  on  evidence  of  this  kind  that  geological 
time  is  divided  into  stages,  ages,  and  epochs, 
which  record  a  series  of  transitions  and  succes- 
sions, which  the  life  of  a  limited  part  of  the  globe 
has  undergone.  Sometimes  the  diffusion  of  world- 
wide species  appears  to  have  been  as  remarkable 
in  the  seas  of  old  geological  periods,  as  any  geo- 
graphical extension  of  living  species  which  is 
known  at  the  present  day. 


CHAPTER   X. 

THE    ARCHEAN    ROCKS. 

THE  most  ancient  rocks  are  termed  Archean. 
They  consist  chiefly  of  crystalline  schists,  and 
other  crystalline  substances,  such  as  quartzite, 
limestone,  graphite.  Formerly  they  were  gener- 
ally regarded  as  metamorphic.  At  the  present 
day  some  writers  do  not  believe  that  they  are 
crystallized  out  of  ancient  strata,  which  were  ac- 
cumulated in  water.  Nevertheless  they  show  in 
many  localities,  and  especially  in  the  Laurentian 
rocks  of  Canada,  two  constituents  which  may  in- 
dicate a  stratified  origin.  One  is  the  presence  of 
layers  of  crystalline  limestone,  which  is  not  known 
to  originate  in  nature,  except  by  metamorphism  of 
limestone  built  up  by  organisms  which  lived  in 
water.  Secondly,  these  Laurentian  rocks  contain 
an  amount  of  graphite,  which  has  been  stated  to 
be  equal  in  bulk,  if  it  were  all  brought  together, 
to  the  quantity  of  coal  found  in  a  coal-field.  No 
source  upon  the  earth  for  the  carbon  of  which 
graphite  consists  is  known,  except  the  meta- 


THE   ARCHEAN    ROCKS.  79 

morphism  of  vegetable  matter  such  as  forms  coal. 
Existing  coal-fields  show,  in  the  formation  of  an- 
thracite, what  appears  to  be  a  transitional  step 
between  coal  and  graphite,  for  the  percentage  of 
carbon  augments  as  the  other  gaseous  constitu- 
ents of  coal  are  lost  under  the  distilling  action  of 
pressure  and  heat. 

If  the  Archean  limestones  and  graphite  are  of 
organic  origin,  they  would  appear  to  have  been 
originally  beds  of  coal  and  limestone  which  con- 
sisted mainly,  if  not  entirely,  of  fossils.  There- 
fore, the  other  constituents  of  these  rocks,  the 
schists  which  form  the  great  mass  of  the  country 
north  of  the  St.  Lawrence,  would  appear  once  to 
have  been  sands  and  clays  in  which  fossils  may 
have  been  distributed  as  they  are  in  more  recent 
deposits. 

The  estimated  thickness  of  the  Laurentian  and 
overlying  Huronian  rocks  is  about  50,000  feet, 
and  in  that  thickness  no  fossil  is  found,  unless  the 
structure  named  Eozoon  canadense  which  has  been 
described  from  Laurentian  limestones  is  correctly 
identified  as  an  encrusting  reef-building  foramini- 
fer  ;  which  its  mode  of  occurrence  in  the  rocks 
makes  not  improbable,  though  the  structure  is 
paralleled  in  volcanic  rocks.  Such  metamorphism 
of  ancient  sediments  all  over  the  globe  must  be 
inferred  to  have  obliterated  all  records  of  the 
early  history  of  the  earth. 

The  geological  story  commences  at  a  com- 
paratively late  period,  compared  with  the  unre- 
corded epochs  which  have  gone  before.  Without 
such  an  obliteration  of  a  past  record  of  almost 
infinite  duration  as  compared  with  known  geo- 
logical time,  it  is  inconceivable  that  processes  of 
variation,  such  as  are  now  known  to  be  in  opera- 


8o  THE   STORY   OF   THE   EARTH. 

tion,  can  have  given  rise  to  the  diverse  types  of 
life,  which  the  oldest  fossiliferous  rocks  make 
known. 

The  Archean  rocks  are  widely  spread  on  the 
surface  of  Scandinavia,  Finland  and  North-West 
Russia,  Saxony,  and  Bohemia,  and  in  Bavaria  as 
well  as  in  the  British  Islands.  Rocks  of  this  class 
will  probably  be  found  all  over  the  globe,  wher- 
ever there  is  an  opportunity  of  examining  the  ma- 
terial upon  which  the  most  ancient  fossiliferous 
rocks  rest. 

In  the  Western  Highlands  in  Scotland,  from 
Cape  Wrath  southward,  the  schists  and  funda- 
mental gneiss  of  that  region  are  displaced  by  an 
incredible  multitude  of  horizontal  thrusts  which 
break  them  up  into  parallel  sheets,  almost  as  well 
marked  as  planes  of  stratification,  with  which  they 
were  at  one  time  confused.  Among  these  crys- 
talline rocks  are  included  great  thicknesses  of 
sandstones,  and  folded  in  among  them  occasion- 
ally are  fossiliferous  bands  of  limestone. 

Other  archaean  areas  are  exposed  further 
southward.  The  most  interesting  are  the  crys- 
talline rocks  about  St.  David's,  in  Pembroke- 
shire;  at  the  Longmynd,  in  Shropshire;  in  the 
central  axis  in  Carnarvonshire  ;  and  in  Anglesey. 
In  these  most  ancient  British  rocks,  evidences 
appear  to  exist  of  contemporaneous  activity  of 
terrestrial  volcanos,  so  that  among  the  oldest 
British  rocks,  alternating  with  schists,  are  the 
rhyolite  lavas  of  Bangor,  Carnarvon,  Llyn  Pa- 
darn,  associated  in  some  of  these  localities  with 
.agglomerates.  The  Wrekin  and  Ercal  Hill  make 
known  rhyolites  of  pre-Cambrian  age  which  are 
.associated  with  indurated  volcanic  ash.  In  the 
neighbourhood  of  St.  David's  the  rhyolitic  lavas 


CAMBRIAN   AND  ORDOVICIAN   ROCKS.  8 1 

are  in  the  same  way  associated  with  volcanic  ash, 
interstratified  in  schists,  the  whole  being  affected 
by  compression  to  which  they  have  since  been 
subjected. 

The  British  Geological  Record  begins  with 
conditions  which  indicate  volcanic  outbursts, 
and  the  shallow  water  accumulation  of  grits  and 
pebble  beds.  As  far  as  the  evidence  goes,  similar 
conditions  might  exist  at  the  present  day  ;  but 
the  rocks  have  been  modified  from  their  original 
state  by  slow  chemical  changes. 


CHAPTER   XL 

CAMBRIAN    AND    ORDOVICIAN    ROCKS. 

THERE  is  an  unconformity  between  the  pre- 
Cambrian  and  Cambrian  rocks,  which  implies  a 
long  interval  of  time,  unrepresented  by  deposits 
in  the  localities  which  have  been  examined.  The 
Cambrian  rocks  are  of  enormous  thickness;  and 
in  Britain  are  probably  not  less  than  30,000  feet 
thick  in  Wales  and  the  border  counties  of  Eng- 
land. 

There  is  difference  of  opinion  as  to  the  use 
of  the  term  Cambrian.  Some  writers  make  it 
include  four  groups  of  rocks,  named  Longmynd 
rocks,  Menevian  beds,  Lingula  flags,  and  Tre- 
madoc  slates.  Others  carry  the  name  higher 
and  make  it  include  the  succeeding  rocks  named 
Arenig,  Llanvirn,  Lower  Bala  and  Middle  Bala 
and  Upper  Bala,  which  have  also  been  grouped 
as  Ordovician. 

The  overlying  strata,  termed  May  Hill  rocks, 


82  THE  STORY  OF  THE   EARTH. 

the  Denbighshire  grits,  Wenlock  and  Ludlow  beds, 
and  the  Downton  sandstone  series,  are  combined 
to  form  the  Silurian  group. 

From  the  physical  history  of  the  deposits, 
there  is  ground  for  dividing  the  rocks  in  this 
way,  but  from  consideration  of  the  life  they 
contain,  the  whole  might  well  be  combined,  and 
grouped  together  as  ten  successive  series,  with 
ten  distinct  fauna,  which  more  or  less  resemble 
the  life  of  similar  natural  history  provinces, 
superimposed  on  each  other,  and  preserved  suc- 
cessively in  sediments  in  the  same  area. 

At  first  the  old  rocks  which  comprise  the 
Longmynd  groups,  and  the  Harlech  and  Llan- 
beris  slates,  which  rise  1600  feet  above  the  sea, 
in  the  Longmynd  Hills  in  Shropshire,  consist  of 
slates,  sandstones,  grits,  and  conglomerates;  with 
very  few  fossils.  The  water-worn  pebbles  in  them 
prove  deposition  under  ancient  shore  conditions ; 
and  they  are  associated  with  beds  which  show  the 
ripples  of  waves,  runnels  of  rills  on  the  shore,  in- 
terlacing cracks  formed  by  the  heat  of  the  sun, 
prints  of  raindrops,  and  burrows  of  sea-worms 
closely  allied  to  the  living  Arenicola.  Few  fossils 
have  been  found  in  the  Longmynd.  They  are 
scarcely  more  numerous  in  the  Bangor  country  of 
Carnarvonshire.  There  the  rocks  are  represented 
by  green  and  purple  slates,  which  stretch  from  the 
banks  of  the  Ogwen  through  the  lake  of  Llanberis, 
and  the  Penrhyn  slate  quarries.  In  South  Wales, 
in  the  section  near  St.  David's,  the  interest  of 
these  rocks  is  greatest.  The  conglomerates  and 
sandstones  found  there,  with  red,  purple,  and 
green  slates,  appear  to  be  on  the  same  geo- 
logical horizon  as  the  Bethesda  and  Llanberis 
slate  quarries.  Towards  the  base  of  this  group 


CAMBRIAN   AND   ORDOVICIAN  ROCKS.  83 

of  rocks  are  found  two  genera  of  fossils  named 
Lingulella  and  Discina,  which  may  be  regarded  as 
having  survived  through  all  subsequent  ages  of 
geological  time  to  the  present  day  without  under- 
going any  notable  change,  although  the  surviving 
shell  is  named  Lingula  instead  of  Lingulella.  The 
lowest  beds  in  which  they  occur,  the  Caerfai  group, 
are  succeeded  by  the  Solva  group,  in  which  genera 
of  the  extinct  order  of  Trilobites  appear  in  profu- 
sion. 

Here  occurs  the  oldest  known  sponge  named 
Protospongia,  and  a  species  is  met  with  of  the  ex- 
tinct genus  of  Pteropod  named  Theca,  which  sur- 
vived in  the  ancient  seas  for  a  long  time.  This 
assemblage  of  life,  the  earliest  as  yet  known  in 
the  earth's  history,  consists  of  types  which  are  in 
no  sense  embryonic.  It  distinctly  points  to  a 
line  of  similar  ancestors  which  has  yet  to  be  dis- 
covered. With  the  succession  of  the  overlying 
Menevian  beds,  and  the  succeeding  divisions  of 
the  Lingula  flags  and  Tremadoc  slates,  a  fauna 
of  185  species  of  fossils  becomes  known  in  which 


FIG.  9. — Section  through  North  Wales  from  the  Cambrian  slates 
of  the  Snowdon  district  to  the  Cheshire  Trias. 

some  of  the  shells,  species  of  the  genera  of  Brachi- 
opoda  named  Lingula  and  Orthis,  and  Obolella  pass 
up  into  the  overlying  Arenig  rocks.  With  the, 
Menevian  beds  the  most  ancient  Echinoderm 
appears.  It  is  a  far-off  relative  of  the  existing 
stone-lines  and  sea-eggs.  It  belongs  to  the  ex- 
tinct group  of  Cystidea,  and  is  named  Protoeystites. 


84  THE   STORY   OF   THE   EARTH. 

The  most  ancient  bivalve  shells  known  are  found 
in  the  Tremadoc  rocks  of  Wales.  They  can  be 
closely  paralleled  at  the  present  day.  Modiolopsis 
Nis  probably  nothing  but  Modiola,  the  horse  mussel 
under  another  name  ;  and  Glyptarca,  Palaarca,  and 
Ctenodonta  are  only  forms  of  the  living  genus  Area, 
in  which  the  shell  has  not  developed  the  habit  of 
growing  in  depth  along  its  hinge,  as  in  most  of  its 
living  representatives.  Pteropods  are  well  repre- 
sented :  the  univalve  Gasteropods  are  represented 
by  the  extinct  genus  Bellerophon,  which  appears  to 
be  a  symmetrical  shell  abundant  in  the  primary 
rocks,  probably  allied  to  the  living  Pleurotomaria. 
The  group  of  many-chambered  shells  named  Ceph- 
alopoda is  represented  by  allies  of  the  Nautilus, 
one  of  them  the  straight  horn  Otthoceras,  and  an- 
other Cyrtoceras,  the  curved  horn.  In  the  lower 
Tremadoc  rocks  the  oldest  known  starfish  is 
found,  in  a  species  of  the  genus  P alceasterina j 
and  the  oldest  known  Crinoid  or  Stone-lily,  in  a 
species  of  the  genus  Dendrocrinus. 

The  great  Arenig  series  rests  conformably  on 
the  Tremadoc  slates.  It  forms  Cader  Idris,  the 
Festiniog  Mountains,  Aran  and  Arenig.  It  in- 
cludes a  great  group  of  roofing  slates  worked  in 
the  quarries  of  Festiniog,  and  an  immense  quan- 
tity of  volcanic  ash.  The  total  thickness  of  the 
ashes,  agglomerates  and  lavas  seen  in  Cader  Idris 
is  between  5000  and  6000  feet.  The  throats  of 
the  ancient  volcanos  which  contributed  so  largely 
to  form  the  Arenig  rocks  in  North  Wales,  were 
placed  near  Dolgelly,  and  Aran  Mowddwy  by  the 
late  Sir  A.  Ramsay. 

The  Cambrian  period  was  an  epoch  of  vigor- 
ous volcanic  action.  The  products  of  the  vol- 
canos are  seen  in  the  Skiddaw  slates  of  the  Lake 


CAMBRIAN   AND   ORDOVICIAN   ROCKS.  85 

district,  where  about  12,000  feet  of  volcanic  ash 
and  Andesite  lavas,  of  Honister  Crag  and  Sea- 
thwaite,  mark  the  beginning  of  volcanic  action 
which  continued  through  the  accumulation  of  the 
Borrowdale  series  of  rocks.  In  North  Wales 
Rhyolitic  lavas  continued  to  be  ejected  in  the 
Bala  period  which  followed.  They  are  seen 
about  Bettws-y-coed  and  the  Conway  falls. 
Rhyolitic  lavas  are  seen  in  the  Glyders,  on  the 
north  side  of  the  Pass  of  Llanberis,  near  Bedd- 
Gelert,  and  about  Snowdon. 

The  most  remarkable  feature  in  the  life  of 
these  upper  Cambrian  rocks,  is  the  extraordinary 
abundance  of  the  extinct  group  of  Graptolites. 
They  are  found  not  only  in  South  Wales  and  the 
Lake  District,  but  in  as  great  a  diversity  of  forms 
and  complexity  of  branching  structure  in  North 
America. 

Trilobites  increase  in  number  of  genera  and 
species.  The  genus  Pleurotomaria,  a  Gasteropod 
only  known  at  the  present  day  from  living  species 
in  the  West  Indies  and  verging  on  extinction,  ap- 
pears for  the  first  time  in  the  lower  Arenig  rocks 
at  Llanvirn,  near  St.  Davids.  In  this  period  an- 
other Gasteropod  Euomphalus,  which  continues  to 
be  important  during  the  primary  period,  is  found 
for  the  first  time. 

Several  corals  make  their  appearance  in  the 
Llandeilo  rocks.  They  are  the  most  ancient 
representatives  of  the  group  in  Britain.  Among 
them  is  the  chain  coral  Halysites,  and  a  species  of 
Favosites,  both  of  which  are  important  genera 
in  the  primary  rocks.  The  Crinoids  increase  in 
number. 

Several  genera  of  Brachiopod  shells  appear, 
two  of  which,  Rhynchonella  and  Crania,  afterwards 


86  THE   STORY  OF  THE  EARTH. 

become  much  more  important  and  still  survive; 
while  the  genus  Leptaena,  which  now  first  ap- 
pears, lives  on  till  the  lower  part  of  the  second- 
ary epoch  of  time.  The  common  genus  Mytilus, 
the  edible  mussel,  is  first  found  with  the  close  of 
the  Cambrian  period.  Cephalopods  become  more 
numerous  and  varied,  and  Cystidians  are  repre- 
sented by  a  number  of  genera.  The  appearance 
and  abundance  of  Graptolites,  and  the  increase  of 
Trilobites  in  number  of  genera  and  species,  are 
the  chief  changes  which  occur  in  the  life  of  the 
Cambrian  period  of  time. 

The  Silurian. 

The  Silurian  rocks  extend  unconformably 
over  the  Cambrian  Strata.  Between  the  Long- 
mynd  and  Wenlock  Edge,  they  cover  up  the 
whole  series  of  the  Cambrian  strata,  resting  upon 
their  upturned  and  denuded  edges.  But  when 
they  are  traced  into  North  Wales  in  Denbigh- 
shire, the  evidence  of  Silurian  unconformity  is 
less  marked. 

The  Silurian  rocks  typically  include  the  May- 
hill  sandstone,  the  Wenlock  rocks  and  the  Ludlow 
rocks.  The  May  Hill  series,  so  named  from  May 
Hill  in  Gloucestershire,  consists  chiefly  of  sand- 
stones and  conglomerates,  yellowish  and  brown 
with  oxide  of  iron,  about  1000  feet  thick,  covered 
by  the  Wenlock  group,  which  in  the  south  is 
formed  of  shales  and  limestones,  and  in  Denbigh- 
shire chiefly  of  sandstones  known  as  the  Denbigh 
grits,  which  overlie  the  Tarannon  shales.  Above 
these  rocks  are  the  Ludlow  beds,  which  also  in- 
clude shales  parted  by  the  Aymestry  limestones. 
The  Silurian  group  of  rocks  is  capped  by  the 


SILURIAN   ROCKS.  87 

Downton  sandstone,  which  makes  a  transition  in 
rock  character  to  the  lower  beds  of  the  old  red 
sandstone.  These  Wenlock  and  Ludlow  rocks 
are  the  oldest  British  strata  which  include  con- 
siderable beds  of  limestone.  The  exposure  of 
Wenlock  limestone  at  the  surface  forms  the  hill 
range  south-west  from  Coalbrookdale,  known  as 
Wenlock  Edge. 

These  beds  indicate  shallow-water  conditions 
by  the  May  Hill  sandstones  at  their  base.  The 
shales,  which  are  only  hardened  muds,  were  pre- 


ibC'.  OUL  Rexl  S<x*toT sho'nV 


MAP  OF  AN  INLIER. 

FIG»  10. — Map  showing  a  dome-shaped  elevation  of  Silurian  rocks 
exposed  by  denudation  of  the  old  red  sandstone  and  carbonif- 
erous rocks  which  once  extended  continuously  over  the  whole 
area. 

sumably  deposited  further  from  shore;  while  the 
limestones,  formed  of  corals,  shells,  and  crinoids, 
were  beyond  the  reach  of  sediment,  but  not 
necessarily  formed  in  deep  water. 

The  Wenlock  limestone  includes  a  large  num- 
ber of  corals,  and  is  the  first  indication  met  with 
in  geological  time  of  a  British  coral  reef,  though 
many  of  the  beds  are  largely  composed  of  En- 
crinites,  and  some  of  Brachiopod  shells,  showing 
the  same  conditions  as  are  afterwards  repeated 


88         THE  STORY  OF  THE  EARTH. 

in  the  Carboniferous  limestone,  which  is  locally 
formed  of  many  different  organisms.  There  are 
twenty-five  genera  and  seventy-six  species  of 
corals  in  the  Wenlock  rocks  alone.  And  twenty 
new  genera  of  crinoids  appear,  the  group  being 
represented  by  sixty-eight  species  in  the  Wenlock 
limestone.  This  limestone  is  frequently  thin- 
bedded,  and  alternates  with  shale,  often  green,  as 
is  well  seen  in  the  dome-shaped  exposure  in  the 
Wren's  Nest,  near  Dudley,  where  it  is  covered 
by  coal  measures  without  any  intervening  rocks. 
The  thin  beds  of  limestone  both  in  the  W'enlock 
and  Ludlow  beds,  thin  out,  first  becoming  nodu- 
lar and  concretionary,  and  then  disappearing 
altogether. 

In  Wales  and  the  adjacent  parts  of  England 
the  Wenlock  rocks  have  been  very  little  meta- 
morphosed, and  are  in  this  respect  in  marked 
contrast  to  the  cleaved  slates  of  the  Cambrian 
period.  They  have  probably  a  wide  distribution 
under  the  secondary  strata,  and  were  met  with 
below  the  chalk  and  Gault  at  Ware,  in  a  deep 
boring  for  water.  The  characteristic  fossils  are 
present.  With  the  exception  of  the  remarkable 
crinoids,  corals,  and  brachiopods,  there  is  noth- 
ing very  impressive  in  the  character  of  the  Silu- 
rian fauna.  The  remarkable  Crustacea  Eurypte- 
rus,  Pterygotus,  and  Hemiaspis  first  appear  in  the 
Wenlock  rocks. 

The  oldest  fishes  in  Britain  are  met  with  in 
the  Ludlow  rocks,  represented  by  no  fewer  than 
ten  species.  Among  these  is  the  Buckler-headed 
Scaphaspis  in  the  Lower  Ludlow,  while  in  the 
Upper  Ludlow  are  found  Cephalaspis,  afterwards 
known  in  the  old  red  sandstone,  together  with 
Pteraspis,  Auchenaspis,  Onchus,  and  other  genera. 


SILURIAN   ROCKS.  89 

The  Eurypterida  appear  to  have  reached  their 
maximum  development  in  the  Upper  Ludlow 
period.  There  were  probably  more  fishes  living 
then  than  are  yet  known,  since  the  Ludlow  bone 
bed,  which  is  found  all  round  the  Woolhope  area, 
at  May  Hill,  and  in  many  other  localities,  consists 
largely  of  the  remains  of  fishes  matted  togeth- 
er, with  fragments  of  the  great  Crustacea,  some 
plants,  and  some  shells.  The  Downton  sand- 
stones and  Ledbury  shales  especially  abound 
with  the  remains  of  Eurypterus  and  Pterygotus. 
With  the  Ludlow  beds,  trilobites  become  less 
important,  and  genera  which  occur  in  the  upper- 
most Ludlow  beds  are  also  met  with  in  the 
Devonian  rocks.  The  wide-spread  crustacean 
type,  Eurypterus,  is  largely  represented  in  Scot- 
land. All  the  compound  graptolites  vanish,  and 
the  group  disappears  with  a  few  simple  species 
in  the  lower  Ludlow  beds.  Ludlow  rocks  yield 
a  considerable  number  of  star-fishes,  partly  from 
Westmoreland,  partly  from  Ludlow.  Orthoceras 
is  known  from  a  multitude  of  species ;  and  there 
are  allied  genera. 

The  organisms  known  in  the  lower  Palaeozoic 
rocks  make  up  an  enormous  fauna,  with  multi- 
tudes of  genera  of  sponges,  corals,  hydrozoa, 
crinoids,  cystidians  and  star-fishes,  trilobites, 
phyllopods,  eurypterida,  and  every  group  of 
mollusca,  as  well  as  many  fishes.  It  is  in  this 
period  of  time  that  the  "  sea-eggs,"  with  flexible 
and  elastic  enveloping  shells  make  their  first  ap- 
pearance in  British  rocks,  in  the  genus  Palcechinus. 
They  are  of  spheroidal  form,  and  composed  of 
numerous  plates  in  rows  which  overlap  each  other 
obliquely  at  the  edges.  The  group  is  always 
scantily  represented  in  the  geological  deposits, 


90  THE   STORY  OF  THE   EARTH. 

but  still  survives  in  the  deep  oceans,  where  it  is 
represented  by  the  genus  Calveria  dredged  in  445 
fathoms  of  water. 


Trilobites. 

Trilobites  are  a  group  of  Crustacea,  entirely 
extinct,  which  appear  in  the  oldest  stratified  rocks, 
and  survive  till  the  close  of  the  carboniferous 
period.  The  group  is  characterised  by  having 
the  body  divided,  first  into  a  head-shield,  termed 
the  cephalo-thorax,  which  may  theoretically  con- 
sist of  five  segments  of  the  immature  animal, 
blended  into  one  plate.  In  this  shield,  in  a  suture 
between  the  central  part  called  the  glabella  and 
the  free  cheeks,  the  eyes  are  placed,  when  the 
eyes  have  a  recognisable  development.  Some 
trilobites  appear  to  be  blind,  being  without  eyes. 
On  the  under  side  of  the  head  is  the  labrum,  from 
which  the  long-jointed  antennae  extend  forward  in 
a  genus  named  Triarthrus.  The  middle  part  of 
the  animal,  known  as  the  abdomen,  consists  of  a 
number  of  separate  overlapping  plates,  like  those 
in  the  tail  of  a  lobster,  which  are  capable  of  mov- 
ing freely  upon  each  other,  and  are  sometimes 
arranged  so  that  the  animal  can  roll  into  a 
ball,  like  the  living  terrestrial'crustacean  Oniscus, 
known  as  the  woodlouse.  The  number  of  these 
joints  in  the  abdomen,  termed  somites,  varies  from 
two  in  Agnostus,  to  about  twenty  in  genera  like 
Paradoxides,  which  is  one  of  the  oldest,  and  Aula- 
copleura,  which  is  a  Silurian  type.  Thirdly,  there 
is  a  tail-plate,  known  as  the  pygidium,  which  is 
sometimes  marked  with  external  ornament,  cor- 
responding to  that  of  the  separate  plates  of  the 
abdomen,  and  sometimes  smooth.  The  eyes  are 


SILURIAN   ROCKS. 


compound,  and  the  individual  facets  can  be  seen 
with  a  lens,  and  although  generally  grouped  to- 
gether and  raised  in  a  crescent,  as  in  the  genus 
Phacops,  appear  sometimes  to  be  scattered,  so  as 
to  cover  much  of  the  lateral  plates  of  the  cephalo- 
thorax,  as  in  the  genus  Trinudeus.  The  intestine 
is  sometimes  preserved.  On  the  under  side  of  the 
body  numerous  limbs  were  developed. 

On  the  head,  besides  the  antennae,  there  were 
appendages  for  mastication,  but  only  one  of  them 
is  preserved.  The  jointed 
limbs  on  the  trunk  consist  of 
two  parts,  one  for  locomo- 
tion, and  the  other  a  gill ;  so 
that  they  appear  to  belong 
to  the  leaf-footed  group  of 
Crustacea  termed  Phyllo- 
pods,  notwithstanding  their 
remarkable  external  resem- 
blance to  the  king  crabs,  to- 
wards which  they  approxi- 
mate. 

The  limbs  gradually  di- 
minish in  size  from  front  to 
back,  where  the  hindermost 
are  minute  and  rudimentary. 

The  two  longitudinal 
grooves  make  the  three 
lobes  of  a  Trilobite. 

The  most  ancient  Trilo- 
bites  include  the  simplest  and  some  of  the  most 
complex.  They  vary  chiefly  in  the  number  of 
segments;  the  form  and  size  of  the  cephalo-tho- 
rax,  and  the  pygidium ;  in  the  elongation  of  the 
pleurae  of  the  abdomen  ;  in  the  external  ornament 
of  the  carapace,  which  sometimes  takes  the  form 


TRIARTHRUS. 
FIG.  ii. — A  Trilobite  show- 
ing feet  and  antennas. 


92  THE  STORY  OF  THE   EARTH. 

of  spines  upon  all  parts  of  the  body.  As  the 
Trilobite  grows  it  is  said  to  shed  its  shell  like 
other  Crustacea  ;  and  with  this  growth  there  come 
to  be  additional  plates  added  to  the  abdomen,  so 
that  there  is  a  sense  in  which  the  ancient  types, 
like  Paradoxides,  may  be  regarded  as  the  most 
complex. 

Among  the  Lower  Cambrian  genera  are  Para- 
doxides,  Dikelocephalus,  Olenus,  Conocoryphe.  In 
the  middle  and  Upper  Cambrian  or  Ordovician 
rocks,  the  common  genera  include  Ogygia,  Asa- 
phus,  Trinucleus,  Lichas,  Acidaspis.  Phacops 
ranges  through  the  Silurian  and  Devonian ;  and 
Iliaenus  ranges  from  the  Upper  Cambrian  to  the 
Silurian. 

In  the  Silurian,  Calymene,  Encrinurus,  Phacops ', 
and  Homalonotus  are  characteristic  genera. 

In  the  Devonian  rocks,  Phacops,  Homalonotus 
and  Bronteus  are  commonest. 

In  the  carboniferous,  Phillipsia  is  the  best- 
known  genus. 


CHAPTER   XII. 

OLD    RED    SANDSTONE    AND    DEVONIAN    PERIOD. 

A  GREAT  unconformity  is  inferred  to  divide 
the  Silurian  rocks  below  from  the  overlying 
strata.  North  of  the  Bristol  Channel  there  is  no 
evidence  of  marine  origin  for  the  deposits  which 
appear  to  have  been  accumulated  in  great  lakes 
upon  a  land  surface.  South  of  the  Bristol  Chan- 
nel, and  eastward  through  France  and  Germany, 
the  rocks  which  follow  upon  the  Silurian  are 
entirely  marine.  They  are  remarkable  for  the 


OLD  RED  SANDSTONE  AND  DEVONIAN  PERIOD.      93 

circumstance  that  the  lowest  beds  exposed  give 
evidence  of  shallow-water  conditions  in  con- 
glomerates and  sandstones,  seen  in  North  Devon 
and  West  Somerset,  in  the  beds  known  as  the 
Foreland  and  Linton  group.  In  South  Devon 
the  lowest  beds  are  purple  slaty  rocks.  The 
middle  or  Ilfracombe  group,  though  mainly 
formed  of  slaty  rocks,  contains  a  little  limestone. 


CARBONIFEROUS 

W.  E. 

FIG.  12. — Section  from  west  to  east,  showing  how  the  Silurian, 
Old  Red  Sandstone,  and  Carboniferous  rocks  are  folded  be- 
tween South  Wales  and  Gloucestershire. 

The  limestone  becomes  more  abundant  in  South 
Devon  at  Plymouth  and  Torquay,  often  taking 
the  form  of  great  coral  reefs  and  sometimes 
thinning  off  into  the  shales.  The  uppermost 
Devonian  known  as  the  Pilton  group  in  North 
Devon  becomes  sandstone.  In  Cornwall  these 
rocks  are  represented  by  limestones  and  slates  at 
Petherwyn. 

The  striking  feature  of  these  rocks  is  the 
remarkable  change  which  takes  place  in  the 
marine  life.  The  multitude  of  genera  which  had 
survived  more  or  less  conspicuously  from  the 
Cambrian  to  the  Silurian  time  becomes  replaced 
by  new  sets  of  types  which  are  substantially  the 
same  as  survive  through  the  marine  beds  of  the 


94  THE  STORY  OF  THE   EARTH. 

carboniferous  period.  Some  layers  are  character- 
ized by  a  few  peculiar  genera,  such  as  the  conti- 
nental deposits  in  the  Middle  Devonian  known 
from  the  Brachiopod  Stringocephalus,  as  Stringo- 
cephalus  limestone ;  and  from  the  coral  Calceola 
as  Calceola  slate,  which  give  a  distinctive  char- 
acter to  the  Devonian  period.  It  is  in  the 
Devonian  age  that  we  are  particularly  impressed 
with  the  abundance  on  the  earth  of  types  of  life 
which  enter  largely  into  the  existing  fauna. 

Fishes  have  hitherto  been  few  in  number,  but 
some  of  those  remarkable  fishes  Pterichthys  which 
occurred  at  the  top  of  the  Ludlow  beds,  together 
with  Coccosteus  and  the  great  scaled  fringe-tinned 
Holoptychius,  are  found  in  the  marine  Devonian 
beds  of  the  continent,  as  well  as  in  the  old  red 
sandstone  of  Scotland. 

In  this  period  commence  several  marine  uni- 
valve shells  such  as  Natica,  Nerita,  Trochus, 
Vermetus,  which  are  so  important  in  the  sea-shore 
life  of  the  present  day. 

They  are  associated  with  two  very  interesting 
Cephalopods.  Nautilus  occurs  accompanied  by 
the  remarkable  Nautiloid  shell  named  Clymenia, 
which  has  a  fold  in  each  septum  which  divides 
one  chamber  from  another,  similar  to  the  fold 
which  is  observed  in  the  septa  of  many  tertiary 
species  of  Nautilus,  which  are  similarly  com- 
pressed from  side  to  side.  Those  compressed 
tertiary  species  have  the  little  tube  named  the 
siphuncle  which  passes  through  the  septa  placed 
in  a  more  inward  position  than  is  usual  in  Nau- 
tilus. This  genus  Clymenia  has  the  siphuncle  as 
far  inward  as  it  could  be,  so  as  to  be  in  contact 
with  the  previously  formed  coil.  The  genus  is 
therefore  in  marked  contrast  to  another  remarka- 


OLD  RED  SANDSTONE  AND  DEVONIAN  PERIOD.      95 

ble  fossil  named  Goniatites,  in  which  the  septa  are 
angularly  folded  several  times,  and  the  siphuncle 
is  as  far  outward  as  it  can  be.  Goniatites  is  the 
antecedent  form  of  the  great  group  of  Cephalopod 
shells  allied  to  Ammonites,  which  is  found  in  the 
Secondary  strata. 

On  turning  landward  to  the  lacustrine  deposits 
of  Old  Red  Sandstone  age,  the  first  of  the  great 
lakes  in  the  British  area  on  which  the  old  red 
sandstone  was  deposited,  is  that  which  extends 
from  Coalbrookdale  southward  over  Hereford 
and  Monmouth,  and  westward  into  Pembroke- 
shire. The  sandstone  accumulated  in  it  is  esti- 
mated to  be  about  8000  feet  thick  in  Hereford 
and  Brecon  ;  and  in  Monmouth  it  includes  thick 
conglomerates,  full  of  quartz  pebbles,  which  may 
be  compared  with  those  which  formed  the  Mill- 
stone Grit,  in  a  later  period  of  time.  The  lower 
part  of  this  area  of  the  Old  Red  Sandstone  is 
termed  the  cornstone  group. 

As  might  be  expected  there  is  an  overlap  of 
these  beds  upon  the  Upper  Cambrian,  which  is 
well  seen  near  Caermarthen. 

Some  of  the  marine  fossils  found  in  the  De- 
vonian of  North  Devon  are  also  met  ''with  in 
Pembrokeshire.  Hence  there  is  some  ground  for 
believing  that  the  old  red  sandstone,  which  is 
assumed  to  have  been  lacustrine,  communicated 
with  the  sea  by  an  estuary.  This  may  account 
for  the  occurrence  of  some  fishes  indifferently  in 
the  marine  and  fresh-water  beds,  which  are  now 
separated  approximately  by  the  Bristol  Channel. 

All  the  other  old  red  sandstone  deposits  are  re- 
garded as  formed  in  lakes,  chiefly  in  the  lower 
old  red  sandstone  period.  These  supposed  lakes 
have  been  named  from  the  geographical  regions 


96  THE   STORY  OF   THE   EARTH. 

which  the  rocks  occupy.  First,  Lake  Cheviot  in- 
cludes the  Cheviot  Hills  with  considerable  thick- 
nesses of  volcanic  rock  of  the  kind  named  Por- 
phyrite  or  Andesite.  Further  north  a  great  lake, 
termed  Lake  Caledonia,  appears  to  have  extended 
southward  from  the  Grampians  over  the  Firth  of 
Clyde  into  the  North  of  Ireland.  Third,  the  lake 
of  Lome  covered  part  of  Argyleshire  from  Loch 
Awe,  and  may  have  extended  northward  in  the 
line  of  the  great  glen.  Further  north  still  is  the 
old  red  sandstone  region  beyond  the  Grampians, 
which  includes  Caithness  and  Sutherland,  the  Ork- 
neys and  Shetlands.  The  lake  is  named  Lake 
Orcadie.  It  is  filled  with  conglomerates,  red  sand- 
stone and  grey  flagstones,  with  occasional  thin- 
bedded  limestones,  sometimes  bituminous  in  the 
upper  part. 

In  these  beds  there  are  many  terrestrial  plants, 
some  coniferous,  and  some,  such  as  Lepidodendron 
and  Calamites,  like  those  of  the  Coal,  and  similar 
to  the  plants  found  in  the  upper  Devonian  rocks 
of  North  Devon,  probably  derived  from  the  land 
to  the  north.  Pterygotus,  which  had  appeared  in 
the  marine  Silurian  beds,  is  well  known  in  the 
old  red  sandstone  of  Scotland,  where  it  has  been 
termed  by  quarrymen  "  fossil  seraphim." 

The  fishes  are  of  extreme  interest.  First,  there 
is  the  remarkable  extinct  group  of  buckler-headed 
fishes  represented  by  Plerichthys  and  Cephalaspis. 
Secondly,  the  more  remarkable  series  of  fringe- 
finned  fishes  termed  Crossopterygidse,  which  are 
represented  at  the  present  day  by  Polypterus  of  the 
river  Nile.  These  fishes  are  covered  with  bony 
armour,  and  include  a  great  number  of  types  such 
as  Osteolepis,  Holoptychius,  Dipterus. 

These  fishes  do  not  appear  to  be  in  any  sense 


CARBONIFEROUS.  97 

embryonic.  They  have  great  importance  in  the 
primary  period.  One  of  their  living  representa- 
tives, the  Ceratodus,  has,  in  addition  to  the  gills 
which  are  common  to  most  fishes,  a  lung  which  is 
adapted  to  breathing  air  under  terrestrial  condi- 
tions, as  though  it  were  possible  for  some  fishes 
to  have  developed  terrestrial  habits  of  life. 

Another  interesting  circumstance  connected 
with  the  old  red  sandstone  is  the  occurrence  in 
it,  in  the  Irish  locality  of  Kiltorkan,  and  near 
Caerleon  in  Monmouth,  of  a  shell,  which  has  not 
been  distinguished  from  the  common  pond  mussel, 
named  Anodonta. 

Beds  of  the  same  age  in  Canada  make  known, 
among  evidences  of  terrestrial  life,  large  insects; 
and  remarkable  forms  of  myriapods,  in  which 
there  is  only  one  pair  of  legs  developed  on  each 
segment  of  the  body. 

The  accumulation  of  the  enormous  thicknesses 
of  the  old  red  sandstone  deposits  presupposes  im- 
mense dimensions  for  a  lake  in  which  sediments 
three  miles  thick  could  be  piled  up,  and  a  large 
area  of  denudation  to  furnish  it  with  sediments. 


CHAPTER   XIII. 

CARBONIFEROUS. 

THE  carboniferous  period  of  time  has  been  so 
named  because  it  is  the  principal  geological  epoch 
in  Britain  in  which  coal  occurs.  The  rocks  rest 
on  the  Old  Red  Sandstone  in  Scotland,  and  on  the 
Devonian  in  the  west  of  England.  They  are  un- 
conformable  to  the  older  rocks  in  some  districts. 


98         THE  STORY  OF  THE  EARTH. 

The  carboniferous  period,  like  the  preceding 
epoch,  gives  evidence  of  conditions  which  are  in 
part  marine,  and  in  part  terrestrial.  In  the  south- 
ern area,  it  is  the  marine  condition  which  is  chiefly 
developed  in  the  lower  part  of  the  formation. 
Whereas,  in  the  northern  area,  terrestrial  condi- 
tions are  developed  towards  the  base.  In  travel- 
ling southward  from  Scotland  over  Britain  the 
terrestrial  beds  come  to  hold  a  higher  and  higher 
position  among  the  carboniferous  strata.  The 
formation  is  usually  taken  to  include  four  or  five 
chief  divisions,  which,  commencing  at  the  base, 
are  reckoned  as  Lower  Limestone  Shales,  Car- 
boniferous Limestone,  Yoredale  beds,  Millstone 
grit  and  Coal  Measures. 

The  first  point  of  interest  of  this  epoch,  is  in 
the  circumstance  that  in  Scotland,  the  Calciferous 
Sandstone,  which  attains  a  thickness  of  3,500  feet, 
lies  at  the  base  of  the  formation,  so  that  the  sand- 
stone conditions  of  the  carboniferous  period,  suc- 
ceed to  the  sandstone  conditions  of  the  old  red 
sandstone.  There  are  occasional  beds  of  lime- 
stone and  shales,  like  the  Burdiehouse  limestone 
in  the  upper  part  of  the  group.  The  fossils  in- 
clude land  plants.  There  is  evidence  of  consider- 
able volcanic  activity,  especially  in  the  tuffs  and 
andesite  lavas  associated  with  the  calciferous  pe- 
riod, in  the  Garlton  Hills,  north  of  Kaddington. 
In  the  shales  are  one  or  two  coal  seams;  and  the 
shales  themselves  are  sometimes  so  bituminous  as 
to  be  a  valuable  source  of  mineral  oil.  The  ter- 
restrial conditions,  which  commenced  in  this  way 
in  Scotland,  appear  never  to  have  entirely  ceased 
in  any  of  the  areas  in  which  the  coal  is  found. 
There  is  therefore  no  great  break  in  Scotland  in 
conformity  of  physical  conditions  with  the  older 


CARBONIFEROUS.  99 

terrestrial  and  lacustrine  conditions  of  the  old  red 
sandstone  period.  As  the  Calciferous  Sandstone 
is  followed  southward,  it  becomes  represented, 
first  by  the  Tuedian  beds  of  Northumberland  and 
Durham,  which  are  alternations  of  sandstones, 
shales  and  impure  limestones.  There  is  no  Old 
Red  Sandstone  below  the  Carboniferous  rocks  in 
the  North  of  England,  and  from  the  Cheviot  lake 
to  Coalbrookdale,  the  Old  Red  Sandstone  is  doubt- 
fully represented.  In  the  South  Wales  coal  field, 
and  the  Bristol  coal  field,  and  the  country  of  the 
Mendip  Hills,  the  400  or  500  feet  of  Lower  Lime- 
stone Shale,  with  the  bone  bed  at  or  about  the 
base,  consists  chiefly  of  alternations  of  limestone 
and  shale,  more  or  less  charged  with  fish  remains. 
There  is  little  to  separate  the  marine  life  of  this 
period  from  that  of  the  Carboniferous  Limestone. 

The  second  division  of  the  carboniferous  rocks, 
known  as  the  Carboniferous  Limestone  series, 
commences  in  the  Scotch  coal  fields  with  sand- 
stones, shales,  fireclays,  coal  beds  and  a  thin 
bedded  limestone.  The  Scotch  beds  are  grouped 
into  the  lower  limestone  series,  the  edge  coal 
series,  and  the  upper  limestone  series.  The  mid- 
dle, or  edge  coal  division,  is  about  600  feet  thick; 
and  includes  among  the  sandstones  ami  shales 
twenty-six  seams  of  coal,  now  highly  inclined, 
which  grew  where  th§y  are  found,  and  each  is 
more  than  one  foot  thick.  The  coal  beds  are  not 
entirely  absent  from  the  upper  limestone  series, 
so  that  the  representative  of  the  Carboniferous 
Limestone  in  Scotland  is  important,  as  indicating 
terrestrial  conditions  which  are  not  quite  sharply 
marked  off  from  those  of  the  Calciferous  Sand- 
stone below. 

Travelling  southward  a  remarkable  physical 


100        THE  STORY  OF  THE  EARTH. 

change  takes  place.    The  carboniferous  limestone 
consists  of  numerous  alternations  of  limestones 


FIG.  13. — Section  showing  the  strata  on  the  east  of  the  Pennine 
chain. 

with  shales,  which  are  well  exposed  in  the  dales 
of  Yorkshire,  where  they  are  cut  through  by  the 
rivers  draining  eastward  into  the  North  Sea. 
Above  the  limestone  group,  which  is  known  as 
the  Scar  Limestone  or  Mountain  Limestone,  there 
is  a  superimposed  series  termed  the  Yoredale 
beds,  which  are  well  represented  in  Northumber- 
land, Yorkshire  and  Lancashire,  and  are  thickest 
on  the  west  side  of  the  Pennine  chain.  These 
beds  are  partly  sandstone,  termed  Yoredale  grit ; 
but  mainly  shales,  with  impure  limestone;  so  that 
they  form,  essentially,  an  upper  division  of  the 
Carboniferous  Limestone  in  the  North  of  Eng- 
land. In  Derbyshire  and  Flint  the  carboniferous 
limestone  attains  an  immense  thickness.  And 
then  southward,  in  the  West  of  England  and 
South  Wales,  it  is  reduced  to  1000  or  2000  feet, 
with  a  capping  of  Upper  Limestone  Shale,  which 
represents  the  Yoredale  beds. 

Where  the  limestone  is  well  developed,  whether 
in  the  west  of  Yorkshire  or  Derbyshire  or  Bristol, 
its  organic  origin  is  usually  evident.  It  is  formed 
in  some  places  of  the  remains  of  Encrinites,  in 
others  of  Corals,  occasionally  of  Brachiopod 
shells,  while  there  are  a  few  localities,  especially 
in  the  Bristol  area,  where  the  limestone  is  organic 


CARBONIFEROUS. 


101 


in  the  same  sense  as  the  Oolites  are  organic,  con- 
sisting  of  rounded  grains  cemented  together  which 
appear  to  have  originated  in  the  growth  of  marine 
Algae  allied  to  existing  Nullipores. 


Fossils  of  the  Carboniferous  Limestone. 

The  Carboniferous  Limestone  being  in  part  a 
coralline  limestone,  includes  a  large  number  of 
corals.  Probably  the  commonest  genera  found  in 
Europe  are  Amplexus,  Cyathophyllum,  Lithostrotion, 
and  Zaphrentis.  They 
are  numerous  in  species 
and  abundant  in  individ- 
uals, and  are  all  of  ex- 
tinct types. 

The  Echinodermata 
are  largely  represented; 
and  propably  in  no  de- 
posit is  there  a  greater 
number  of  crinoids.  The 
principal  genera  are  Ac- 
tinocrinus,  Cyathocrinus 
and  Platycrinus. 

The  shells,  however, 
are  even  more  distinctive.  The  two  genera  Pro- 
ductus  and  Spirifera  comprise  more  than  half  the 
species  of  Brachiopods.  Rhynchonella  is  well  repre- 
sented in  association  with  Terebratula.  The  latter 
two  survive  all  subsequent  revolutions  of  the  earth. 

Among  the  other  shells,  the  bivalves  Pinna, 
Lima  and  Anomia,  Avicula,  Pecten  are  associated 
with  Modiola,  Mytilus,  Area,  Solenopsis,  Solemya, 
types  which  appear  to  survive  to  the  present  day, 
more  common  on  British  coasts  than  in  the  car- 
boniferous rocks. 


FIG.  14. — Productus,  a  brachio- 
pod  of  the  carboniferous  lime- 
stone. 


102       THE  STORY  OF  THE  EARTH. 

Such  univalve  or  Gasteropod  shells  as  Chiton, 
Littorina,  Natica,  Patella,  Pleurotomaria,  Turritella 
and  Turbo  are  surviving  genera  which  are  found 
in  the  Carboniferous  Limestone.  These  are  not 
always  the  genera  richest  in  species.  Aviculo- 
pecten,  which  is  regarded  as  extinct,  has  more 
species  than  any  other  bivalve ;  and  JSuontfhalus, 
also  extinct,  is  one  of  the  best  represented  genera 
of  gasteropods. 

Fishes  abound,  the  cartilaginous  fishes,  or 
sharks,  appear  curiously  to  parallel  both  in  their 
fin  defences  and  teeth,  the  sharks  which  are  sub- 
sequently found  in  the  Secondary  rocks.  The 
ganoid  fishes  are  also  well  represented.  As  a 
group  they  are  unlike  the  types  which  lived  in 
the  old  red  sandstone  time. 


Millstone  Grit. 

This  rock,  mainly  formed  of  quartz  grains,  is 
a  shallow-water  deposit,  which  often  gives  evi- 

dence of  current  bed- 
ding, and  sometimes  di- 
vides along  planes  in 
which  the  mineral  mica 
is  abundantly  deposited. 
There  is  perhaps  no 
good  ground  for  separa- 
^^^^^^  ting  these  rocks  from 

FIG.  i5.-Pieurotomaria,  show-    the       overlying        coal 
ing  remains  of  the  original    measures  ;  and  the  sand- 

he11- 


tain  are  not  more  im- 
portant than  those  known  as  the  Pennant  sand- 
stones, in  the  coal  measures  of  the  West  of  Eng- 
land. They  resemble  the  coal  measures  of  the 


CARBONIFEROUS.  103 

south  in  the  character  of  their  sandstones  and 
ironstones,  and  they  yield,  in  various  localities, 
some  thin  beds  of  coal. 

In  Scotland  this  third  division  of  the  car- 
boniferous group  of  rocks,  is  named  the  Moor 
Rock.  Its  only  difference  from  the  Millstone 
Grit,  is  in  containing  marine  fossils.  But  this 
condition  probably  only  indicates  that  the  lacus- 
trine basins,  in  which  much  of  the  deposit  may 
have  been  formed,  were  sometimes  open  to  the 
sea.  Southward  in  England,  the  Moor  rock 
known  as  the  Millstone  grit,  consists  chiefly  of 
alternations  of  sandstone  and  shale.  It  is  only 
50  feet  thick  in  Leicestershire  but  thickens  in  the 
west.  In  Northumberland  it  is  400  feet  thick.  In 
the  Forest  of  Dean  it  is  less  than  500  feet.  It  is 
1000  feet  thick  in  the  Somersetshire  coal  field. 
From  this  deposit  a  large  part  of  the  flagstones 
of  Britain  is  obtained.  It  forms  the  wildest  scen- 
ery of  the  western  side  of  the  Pennine  chain.  This 
is  due  to  the  succession  of  the  four  principal  beds 
of  grit  which  rest  upon  each  other  in  successive 
terraces,  with  the  thick  Kinderscout  grit  at  the 
bottom,  and  the  three  less  important  grits  above, 
which  are  all  divided  from  each  other  by  shales 
and  sandstones.  There  are  many  thin 'beds  of 
coal  in  the  Millstone  Grit.  None  of  them  are 
worth  working,  so  that  the  coal  miner  knows  the 
deposit  in  England  as  the  Farewell  rock,  below 
which  coal  is  not  to  be  expected.  The  existence 
of  the  Millstone  Grit  indicates  an  upheaval  of 
the  Carboniferous  Limestone  sea,  by  which  the 
conditions  of  physical  geography  became  simi- 
lar in  England  to  what  they  were  in  Scotland. 
Such  an  upheaval  exposed  the  uplifted  rocks  to 
denudation,  and  probably  furnished  the  material 


104        THE  STORY  OF  THE  EARTH. 

out  of  which    the   millstone   grit    sandstone  was 
made. 

The  thick  deposits  in  the  south  of  England 
are  near  to  the  areas  in  which  the  thick  masses 
of  old  red  sandstone  are  found.  It  is  possible 
that  such  a  cause  has  governed  the  thickness  of 
the  deposit,  though  in  the  west  of  Pembrokeshire 
the  Millstone  Grit  is  only  300  feet  thick  ;  and  it 
is  difficult  to  see  in  areas  now  exposed  any  source 
for  the  Kinderscout  grits,  except  in  such  ancient 
rocks  of  Shropshire  as  form  the  Longmynd,  and 
the  Denbighshire  grits  of  North  Wales.  Denu- 
dation of  the  original  materials  from  which  such 
ancient  rocks  as  those  were  derived  would  have 
made  these  sandstones. 

The  Coal  Measures. 

The  rocks  which  yield  coal  are  a  succession  of 
sandstones,  and  shale,  ironstones,  fire  clays  and 
coal  seams,  which  are  repeated  over  and  over 
again.  They  thicken  from  Northumberland 
south-west  to  South  Wales ;  chiefly  owing  to  in- 
crease in  quantity  of  the  sand.  In  the  north  of 
England  the  thickness  is  1500  feet;  in  the  south- 
west in  Wales  it  is  11,000  feet. 

Fire  clays  are  old  soils  of  the  carboniferous 
land  in  which  the  roots  of  forest  trees  often  stand 
vertical,  as  they  grew;  showing  that  the  coal  was 
in  most  cases  a  peaty  growth,  like  Irish  bogs,  due 
to  the  fall  of  forest  trees,  and  the  accumulation 
of  vegetable  matter  where  the  forest  trees  had 
formerly  grown.  In  South  Wales  scores  of  forest 
trees  of  the  kinds  named  Sigillaria  and  Lepido- 
dendron  may  sometimes  be  seen  crushed  flat  like 
boards,  piled  one  above  another  in  the  positions 


CARBONIFEROUS.  1 05 

in  which  they  fell,  before  they  became  matted 
and  compressed  into  a  solid  mass. 

In  some  cases,  the  coal  growth  has  been  com- 
pared to  the  American  swamps  and  cane-brakes, 
where  the  girdle  of  surrounding  vegetation  filters 
the  muddy  waters,  so  that  only  clear  water 
reaches  the  vegetable  matter  in  the  enclosure. 
There  is  no  doubt  that  carboniferous  land  sur- 
faces were  constantly  undergoing  depression  of 
level,  like  the  Deltas  of  rivers  such  as  the  Po, 
and  the  Mississippi,  in  many  of  which  a  succes- 
sion of  land  surfaces  has  been  found  one  below 
another,  indicating  accumulation  of  sediments 
which  are  similar  to  the  coal  shales  and  sand- 
stones and  resemble  them,  in  the  intercalation  of 
vegetable  growths  between  layers  of  mud.  These 
depressions  during  the  growth  of  the  coal  often 
appear  to  have  been  partial  and  local. 

In  the  Dudley  coal  field  the  lo-yard  seam  is 
found,  which  is  the  thickest  coal  bed  in  England. 
When  it  is  traced  to  the  north,  it  subdivides  into 
nine  seams  of  coal,  each  having  its  own  bed  of 
under  clay,  on  which  successive  forests  grew.  At 
Essington  the  nine  beds  preserve  the  thickness  of 
the  one  bed  at  Dudley,  though  they  have  become 
separated  from  each  other,  by  wedge^  shaped 
layers  of  sandstones  and  shales,  which 'have  an 
aggregate  thickness  of  420  feet. 

The  Dudley  country  is  also  interesting  among 
English  coal-fields  on  account  of  the  volcanic 
eruption,  which  appears  to  have  taken  place  dur- 
ing the  carboniferous  period ;  for  the  basalt  at 
Rowley  Regis,  which  was  ejected  through  the 
coal,  is  in  some  places  in  the  condition  of  cinder 
and  ash  ;  and  this  appears  to  prove  that  it  was 
elected  at  or  near  the  surface.  Volcanic  out- 


106       THE  STORY  OF  THE  EARTH. 

bursts  are  comparatively  rare  in  the  coal  of  Eng- 
land. In  the  Edinburgh  coal-field  the  volcanic 
eruptions  are  the  most  impressive  feature  of  the 
deposit.  The  layers  of  volcanic  ash,  and  vesicu- 
lar lavas,  such  as  may  be  seen  in  Edinburgh,  at 
Calton  Hill,  prove  the  outbursts  to  have  been 
contemporaneous  with  the  sediments.  Regions 
of  volcanic  activity  are  commonly  the  scene  of 
changes  of  level  of  land,  such  as  the  coal  strata 
demonstrate. 

The  layers  of  coal  may  be  compared  to  the 
growth  of  peat  over  the  flat  lands  of  Holland. 
The  sea  sometimes  bursts  in,  as  when  the  Zuyder 
Zee  was  formed,  so  that  marine  beds  with  marine 
shells,  rest  upon  the  terrestrial  growth.  Such 
catastrophes  occurred  in  the  Dudley  coal-field, 
and  more  evidently  in  that  of  Coalbrook  Dale. 
In  the  lower  part  of  the  coal  measures  is  the 
layer  of  clay  ironstone  known  as  the  Pennystone ; 
and  in  the  upper  part  is  the  layer  known  as  the 
Chance  Pennystone;  both  of  these  are  marine  de- 
posits with  marine  fossils,  like  the  shells  Goniatites 
and  Aviculopccttn,  which  had  not  been  seen  since 
the  Carboniferous  Limestone  was  deposited. 
They  were  still  existing  not  far  away  ;  but  might 
have  been  thought  extinct,  but  for  these  incur- 
sions of  the  sea. 

There  is  no  means  of  judging  whether  the 
coal  or  the  intervening  sediments  occupied  the 
longer  time  in  forming.  The  total  thickness  of 
the  coal  in  all  the  seams  added  together,  varies 
from  about  100  to  140  feet. 

The  properties  of  coal  probably  vary  with  the 
nature  of  the  juices  of  the  living  plants.  Thus, 
when  starch  is  burnt  it  gives  a  vesicular  coke  or 
cinder.  When  gum  arabic  is  burned,  it  forms  a 


CARBONIFEROUS.  107 

hard  dull  coke  like  an  imperfectly  coking  coal. 
When  cellulose  is  burnt,  it  forms  a  coke  which 
does  not  cohere,  like  the  substance  known  as 
mother  of  coal.  Hence  differences  which  coals 
show  in  burning  may  depend  upon  the  original 
substance  of  the  plants. 

The  first  important  variety  of  coal  Anthracite, 
which  contains  the  largest  percentage  of  carbon, 
is  clean  to  touch,  and  burns  with  little  smoke. 
In  some  localities  anthracite  appears  to  result 
from  the  distilling  action  of  the  heat  which  is 
generated  underground  by  the  folding  of  the  rocks 
in  a  coal-field.  This  separates  the  mineral  oil 
from  the  coal,  so  that  the  petroleum  escapes  into 
porous  rocks  like  water,  and  may  rise  to  the  sur- 
face in  springs. 

Other  coals  are  often  termed  bituminous,  but 
no  substance  at  all  like  bitumen  exists  in  coal. 
Such  coal  is  insoluble  in  any  of  the  solvents  which 
dissolve  bitumen  ;  but  it  softens  at  a  low  tempera- 
ture. Caking  coals  partly  melt,  and  make  a  com- 
pact coke. 

The  non-caking  coal,  like  the  steam  coal  of 
South  Wales,  does  not  change  its  form  in  burning. 
The  properties  of  the  coals  vary  with  the  different 
beds,  suggesting  differences  in  the  species  of  plants 
which  formed  them. 

The  group  of  rocks  termed  Coal  Measures  is 
commonly  divided  into  three  parts.  The  lower 
coal  measures,  or  Canister  beds,  are  usually  bar- 
ren, or  only  contain  thin  coals,  which  are  not  often 
valuable.  Secondly,  the  middle  coal  measures 
contain  most  of  the  thick  workable  beds  of  coal. 
They  correspond  to  the  Pennant  group  of  South 
Wales  and  the  Bristol  coal-fields.  Thirdly,  the 
upper  coal  measures  yield  a  good  deal  of  coal  in 


108        THE  STORY  OF  THE  EARTH. 

the  South  of  England  and  Wales,  but  mostly  in 
thin  beds. 

The  coal  was  more  widely  spread  in  former 
geological  ages  than  it  is  at  the  present  time, 
though  there  is  no  reason  to  suppose  that  the 
vegetable  growth  ever  extended  continuously  over 
the  country.  The  several  coal-fields  are  basin- 
shaped  depressions,  which  have  been  isolated  from 
each  other,  sometimes  by  denudation.  First  there 
has  been  the  compression  which  elevated  the  Pen- 
nine chain  and  Wales.  This  divided  the  coal-fields 
into  longitudinal  series,  stretching  south  on  each 
side  of  the  Pennine  chain.  Then  the  country  was 
compressed  in  the  opposite  direction,  forming 
folds  which  run  from  east  to  west.  An  upward 
thrust  divides  the  coal-field  of  Northumberland 
and  Durham  from  that  of  Yorkshire  and  Notting- 
ham. Its  effects  are  also  seen  in  the  separation 
of  the  Cumberland  field  from  the  South  Lancashire 
coal-field.  The  folds  which  isolate  the  South 
Wales  and  Forest  of  Dean  coal-fields  and  the 
Somerset  coal-fields  lie  further  south.  Afterwards 
denudation  removed  the  summits  of  the  anticlinal 
folds,  and  the  coal-fields  remained  in  basin-shaped 
depressions. 

Coal  has  been  found  by  boring  beneath  newer 
rocks  at  Burford  in  Oxfordshire;  and  at  Dover; 
so  that  these  east  to  west  folds  of  the  primary 
strata  beneath  the  newer  rocks,  probably  extend 
continuous  with  the  coal  of  Belgium. 

Coal  Plants. 

About  half-a-dozen  terrestrial  plants  which  are 
imperfectly  known,  have  been  described  from 
rocks  older  than  the  Devonian.  The  flora  of  the 


CARBONIFEROUS.  109 

Devonian  period  does  not  differ  essentially  from 
that  of  the  Carboniferous,  since  both  contain  the 
same  genera  of  ferns,  of  giant  reeds  allied  to  the 
living  Equisetum,  and  of  club-mosses  of  the  size  of 
forest  trees,  which  differ  from  the  Quill-wort  and 
Lycopodiums,  more  in  size  than  in  structure. 

The  Carboniferous  period  was  an  age  of  ever- 
green forest  trees  of  types  which  did  not  survive 
the  Permian  period.  No  example  is  known  of 
modern  forest  trees;  but  we  cannot  infer  that 
they  did  not  exist.  The  abundance  of  Eucalyptus, 
and  of  the  leafless  Acacias  in  South  Australia 
shows  how  largely  a  few  genera  may  monopolize 
the  ground ;  and  the  circumstance  that  both  the 
Australian  and  African  floras  are  evergreen  at 
the  present  day,  proves  that  the  absence  of  some 
types  from  a  district  of  the  Earth  or  deposit,  is 
consistent  with  their  existence  at  the  same  period 
of  time  in  another  locality. 

Coniferous  trees  of  the  coal  measures  grew  to 
a  large  size.  In  the  forms  of  their  fruits  they  re- 
semble some  of  the  yew  tribe.  The  living  Sails- 
buria  of  China  has  fruits  which  are  of  nutlike  form, 
and  resemble  the  Coal  Measure  fruits  known  as 
Trigonocarpon  which  are  produced  by  the  forest 
tree  named  Dadoxylon.  Under  the  microscope  the 
wood  of  this  tree  shows  characteristic  coniferous 
structure.  The  tree  differs  from  all  conifers  of 
newer  age  in  having  a  large  central  pith,  formed 
by  a  succession  of  thin  transverse  layers.  Casts 
of  the  pith  cavity  were  long  supposed  to  be  sepa- 
rate plants,  and  named  Sternbergia.  Cordaites  is 
another  conifer  of  the  yew  type.  And  Araucarites 
has  been  so  named  from  its  resemblance  to  the 
living  Araucaria. 

The  club  moss  tribe,  which  at  the  present  day 


HO       THE  STORY  OF  THE  EARTH. 

rarely  grows  erect,  and  never  reaches  a  height  of 
more  than  a  foot  or  two,  is  represented  by  forest 
trees,  which  grew  to  a  height  of  fifty  to  seventy 


FIG.  16. — Part  of  the  trunk  of  a  Sigillaria  from  the  coal  near  Hud- 
dersfield,  showing  the  thin  outer  carbonaceous  layer  with  leaf- 
scars. 

feet.  Like  the  conifers  they  have  become  known 
gradually,  and  each  part  of  the  tree  received  a 
distinct  name,  before  the  structure  was  known 
fully.  In  Sigillaria  the  trunk  is  vertically  grooved, 
with  the  leaf  scars  extending  round  it  in  a  spiral 
pattern.  In  Lepidodendron  each  leaf  scar  is  en- 
closed in  a  lozenge-shaped  area,  and  since  these 


CARBONIFEROUS. 


I  II 


areas  are  in  contact,  the  spiral  pattern  is  more 

marked  than  in   Sigillaria.      The  roots  of  these 

trees  bifurcate  regu- 

larly at    each  subdi- 

vision, and  the  same 

structure  is  found  in 

the    branches   which 

crown      the      trunk. 

The  roots,   formerly 

termed        Stigma  ria  , 

have      an     irregular 

pitted       pattern      of 

scars  to   which   long 

rootlets      were       at- 

tached.      The    fruits 

are  cones,  developed 

like     clubs,    at     the 

ends  of  the  branches. 

These     fruits     were 

termed     Lepidostro- 

bus.       The     existing 

Lycopodium  resembles 

TehifJnJenJrn'n    in    <;nt 
J^epiaoaenaron    in   spl- 

ral  arrangement  of 
the  leaves,  fruiting 
organs  and  spores.  The  internal  structure  is  es- 
sentially the  same.  Lepidodendron  has  a  central 
pith,  surrounded  by  woody  tissue,  which  is  formed 
of  elongated  vessels.  Outside  of  that  is  the  cam- 
bium layer  of  the  bark,  formed  of  large  spherical 
cells,  corresponding  to  the  layer  seen  in  the  quill- 
worts  ;  and  external  to  this  is  the  bark,  formed  of 
small  cells  which  are  elongated. 

Some  of  the  layers  of  coal  which  are  richest 
in  hydrocarbons,  such  as  the  better  bed-coal,  are 
formed  of  spores  of  such  plants.  These  spores 


FlG.  17.—  Part  of  a  frond  of  the  fern 
Teniaeopteris  from  the  Indwe 
coal,  Cape  Colony. 


Ijz        THE  STORY  OF  THE  EARTH. 

are  usually  large  macrospores,  such  as  are  found 
in  the  lower  part  of  the  fruit  of  the  living  Selagi- 
nella ;  and  the  fossil  Triplosporites.  The  fossil 
reeds  of  the  coal,  termed  Catamites,  are  closely 
related  to  the  living  Equisetum,  although  the 
plants  grow  to  a  comparatively  large  size.  Ex- 
ternally the  plant  terminates  downward  in  a  cone. 
The  trunk  is  divided  transversely  by  nodes,  and 
the  internal  cast  of  the  internodes  is  fluted.  At 
the  nodes  the  stem  gives  off  leaves  in  circles,  and 
these  leaves  supported  leaflets  arranged  in  whorls. 
The  leaves  are  known  as  Asterophyliies,  with  needle- 
shaped  leaflets  ;  Annularia,  with  blade-shaped  leaf- 
lets ;  and  Sphenophyllum,  with  wider  wedge-shaped 
leaflets.  There  are  also  several  types  of  fruit, 
which  closely  resemble  the  fruit  of  Equisetum, 
except  that  some  of  the  leaves  do  not  bear  spo- 
rangia, and  thus  form  a  protective  covering  to  the 
others.  The  spores  are  of  the  same  size  in  the 
living  and  fossil  types. 

The  ferns  of  the  coal  known  under  such 
names  as  Alcthopttris,  Neuropteris,  Odontopteris, 
Sphenopteris^  closely  resemble  existing  ferns,  in  so 
far  as  can  be  determined;  for  the  fructification  is 
not  often  preserved.  Four  of  the  eight  existing 
families  of  ferns  are  known  in  the  coal  measures. 
Tree  ferns  have  been  described. 

Animals  of  the  Coal  Forests. 

Terrestrial  shells  are  not  preserved  in  many 
geological  deposits,  and  only  two  genera  are 
"known  from  the  Coal  Measures.  They  are  both 
small,  and  were  found  in  a  bed  of  underclay,  in 
a  layer  about  two  inches  thick,  in  Nova  Scotia, 
probably  swept  down  by  the  rain,  as  shells  in  a 


CARBONIFEROUS.  113 

forest  often  are  at  the  present  day.  One  of  these 
shells  is  a  thin  variety  of  the  common  hedge 
shell  of  Great  Britain,  named  Helix.  The  second 
appears  to  be  identical  with  the  existing  genus 
Pupa,  which  is  commonly  found  about  the  roots 
of  trees.  They  are  the  oldest  terrestrial  shells 
known. 

Associated  with  the  land  shells  are  centipedes. 
The  group  of  Myriapods  to  which  they  belong  is 
distinguished  by  having  one  pair  of  antennae,  eyes 
nearly  always  simple,  no  distinct  thorax,  and  no 
wings;  while  limbs  are  attached  to  nearly  all  the 
segments.  Like  insects  they  have  three  pairs  of 
jaws.  The  respiration,  as  in  insects,  is  carried  on 
by  tracheae,  which  open  near  the  articulations  of 
the  legs,  except  in  the  living  genus  Peripatus. 
Myriapods  live  in  the  loose  bark  of  trees,  in 
cracks  in  the  rock,  and  under  stones.  The  oldest 
forms  were  found  in  the  hollow  trunks  of  Sigil- 
laria.  They  are  Millipedes  rather  than  centi- 
pedes. They  are  known  in  the  carboniferous 
rocks  of  Canada.  A  Millipede  found  in  the  coal 
of  Ayrshire,  named  Euphoberia,  is  four  inches- 
long,  nearly  a  quarter  of  an  inch  broaji,  formed 
of  thirty-six  body  rings,  each  with  two  pairs  of 
legs.  These  myriapods  are  distinguished  by  pos- 
sessing branched  spines  which  are  hollow.  The 
American  genus  Xylobius  has  been  found  at  Glas- 
gow and  Huddersfield,  in  the  coal. 

The  spiders  of  the  coal  belong  to  a  group 
known  as  the  false  scorpions,  of  which  the  type 
is  the  living  genus  Phrynus.  Eophrynus  Prestwichi 
is  a  well-known,  though  rare  fossil  from  the  iron- 
stone of  Dudley.  It  resembles  spiders  in  having 
four  pairs  of  legs,  and  a  pair  of  palpi  is  seen.  On 
the  under  side  of  the  body  are  the  openings  of 
8 


114        THE  STORY  OF  THE  EARTH. 

six  pairs  of  stomata  from  the  tracheae,  which  are 
developed  as  in  insects.  True  spiders  are  found 
in  the  coal  measures  of  Bohemia,  Silesia,  and  of 
Illinois. 

Another  representative  of  this  group  of  Arach- 
nida  is  the  scorpion,  which  is  represented  by  the 
genus  Eoscorpius.  Scorpions  are  first  found  in 
the  Silurian  rocks.  Eoscorpius  found  in  the  coal 
of  Illinois,  appears  to  be  closely  allied  to  a  living 
Californian  scorpion,  of  the  genus  Buthus ;  though 
the  form  found  in  the  coal  of  this  country  agrees 
best  with  the  genus  Scorpio. 

Insects  are  well  represented  in  the  coal. 
Coleoptera  are  known  from  beetles  named  Cur- 
culioides  and  Troxites.  Grasshoppers  are  found, 
as  are  cockroaches.  Lithomantis  represents  the 
living  leaf-insect  Mantis.  The  white  ant  occurs; 
along  with  a  butterfly.  Carboniferous  insects  are 
chiefly  known  from  the  coal-fields  of  the  continent. 

The  fishes  found  in  the  coal  measures  include 
a  number  of  sharks,  known  from  their  fin  defences 
and  teeth. 

Labyrinthodont  reptilia  are  referred  to  more 
than  twenty  genera.  Many  of  these  are  from  the 
Kilkenny  coal-field,  and  Belgian  coal-field.  The 
remarkable  genera,  Anthracosaurus  and  Loxomma 
from  the  coal-field  of  Northumberland  are  among 
the  largest  of  carboniferous  genera.  They  are 
distinguished  by  having  the  teeth  united  to  the 
jaw,  without  being  in  sockets.  In  some  families 
the  palate  is  covered  with  a  large  bone  in  the 
middle,  named  the  para-sphenoid.  The  skull  is 
sculptured  as  in  crocodiles,  and  contains  some 
bones  which  are  not  found  in  existing  reptiles, 
especially  behind  the  eye,  where  bone  is  absent 
in  a  crocodile. 


PERMIAN.  115 

CHAPTER   XIV. 

PERMIAN    AND    TRIAS. 

THE  deposits  which  rest  next  in  succession 
upon  the  Carboniferous  series  are  termed  Permi- 
an, because  they  appear  to  be  identical  with  the 
strata  found  in  the  Russian  government  of  Perm. 
They  had  been  termed  Poikilitic,  or  variegated 
rocks;  and  sometimes  the  Pontefract  rocks,  from 
occurrence  at  that  town  in  Yorkshire. 

Marine  beds  in  the  east  of  England  represent 
them  between  Hartlepool  and  Nottingham,  but 
the  Permian  sandstones  have  sometimes  been 
regarded  as  fresh-water  and  lacustrine  deposits 
in  the  west  and  south-west  of  England.  They 
appear  to  be  unconformable  to  the  underlying 
strata  in  some  localities.  In  other  localities 
there  is  no  clear  separation  between  the  lower 
Permian  rocks  and  the  Carboniferous.  Such 
conditions  appear  in  Lancashire  and  Cheshire, 
and  are  regarded  as  occurring  in  Russia,  and 
in  North  America. 

The  lower  sandstones  in  Cumberland  yield 
the  characteristic  genera  of  Carboniferous  plants. 
It  is  therefore  interesting  that  near  Enville 
in  Worcestershire,  and  in  other  localities,  the 
Permian  rocks  contain  angular  boulders,  which 
are  polished,  and  scratched  apparently  by  ice ; 
though  the  scratched  stones  may  not  be  evidence 
that  glacial  conditions  prevailed  in  that  district 
in  the  Permian  period. 

The  Permian  rocks  of  Great  Britain  comprise 
lower,  middle  and  upper  scries.  The  upper  and 
lower  parts  are  sandstones  and  conglomerates,  or 


Il6        THE  STORY  OF  THE  EARTH. 

sometimes  breccia  derived  from  the  Carboniferous 
limestone.  The  middle  portion  is  a  great  wedge  of 
magnesian  limestone,  resting  upon  the  marl  slate, 
600  feet  thick  in  the  east  of  England,  and  10  or 
20  feet  in  the  west.  The  upper  sandstones  and 
clays  with  gypsum,  like  the  lower  beds,  are  thick 
in  the  west  and  thin  in  the  east :  but  are  only 
about  one-fifth  of  the  thickness  of  the  lower 
sandstone.  The  lower  3000  feet  of  variegated 
sandstone  is  identified  with  the  German  rothlie- 
gende.  The  marl  slate  is  identified  with  the 
kupferschiefer,  and  the  zechstein  with  the  mag- 
nesian limestone.  The  lower  Bunter  of  Germany 
has  been  compared  with  the  gypseous  marls  of  the 
Eden  basin  in  Cumberland. 

The  magnesian  limestone  probably  was  origi- 
nally an  ordinary  limestone  formed  of  calcite,  and 
the  carbonate  of  magnesia  was  apparently  infil- 
trated into  it.  There  is  no  more  singular  deposit 
anywhere  to  be  seen  than  the  exposure  of  this 
rock  at  Sunderland,  where  some  of  the  beds  now 
consist  of  radiating  concretions  of  globular  form 
and  variable  size,  giving  the  rock  an  appearance 
of  being  built  of  shot  or  cannon-balls. 

The  Permian  age  was  a  time  of  considerable 
volcanic  activity,  and  interstratified  beds  of  vol- 
canic ash  and  lava  are  well  seen  in  the  country 
about  Exeter,  and  in  Ayrshire,  as  well  as  in 
Germany. 

In  other  parts  of  the  world  the  Permian  forma- 
tion attains  a  great  development  in  thickness,  and 
contains  important  beds  of  coal.  The  Gondwana 
rocks  of  India,  which  are  probably  comparable  to 
the  Permian  of  Russia,  very  closely  resemble  the 
Permian  rocks  of  the  Karoo  in  South  Africa.  Both 
contain  coal,  and  the  flora  is  probably  Permian, 


PERMIAN.  1 1 7 

but  several  of  the  genera  of  ferns  do  not  occur 
in  Great  Britain. 

Among  the  fossils  in  the  marine  beds  between 
Hartlepool  and  Nottingham  the  foraminifera  in- 
clude several  existing  genera.  Neither  the  corals 
nor  crinoids  show  any  remarkable  variation  from 
carboniferous  types,  and  in  a  general  sense  this  is 
true  of  the  shells,  though  a  large  number  of  the 
genera  which  characterise  the  primary  period  are 
absent.  There  are  some  characteristic  genera  of 
fishes  like  Acrolepis,  but  the  most  abundant  fish 
type  is  Palcecniscus. 

Fossil  Reptiles  of  the  Permian. 

The  Labyrinthodont  reptilia,  distinguished  by 
having  teeth  blended  with  the  jaw  bones  without 
being  in  sockets,  are  found  in  some  British  coal- 
fields, and  are  also  known  from  Permian  deposits. 
In  Bohemia  and  in  Saxony  many  small  animals  of 
diverse  forms  occur  ;  some  long  and  snakelike, 
and  others  like  land  salamanders.  Some  of  these 
closely  resemble  fossils  of  the  Kilkenny  coal-field, 
as  well  as  similar  types  from  the  coal-fields  of 
Illinois,  Ohio,  and  Nova  Scotia,  and  are*  referred 
to  the  same  genera.  One  of  these  Bohemian  ani- 
mals, named  Branchiosaurus,  still  preserves  in  the 
fossil  state  a  skeleton  to  the  bony  arches  which 
supported  gills.  This  old  reptile,  like  some  of 
the  ancient  fishes  associated  with  it,  may  have 
breathed  by  gills  as  well  as  lungs,  like  certain  of 
the  living  amphibia.  This  terrestrial  life  makes 
a  close  link  between  the  Permian  and  Carbonifer- 
ous periods. 

The  Permian  rocks  contain  another  extinct 
group  of  animals  named  Anomodontia,  which 


Il8        THE  STORY  OF  THE  EARTH. 

comprises  the  groups  named  Theriodontia,  Dicy- 
nodontia  and  Pareiasauria.  They  are  animals 
with  depressed  bodies  rarely  lifted  high  above 
the  ground  by  their  limbs,  with  relatively  large 
heads,  and  types  of  dentition  which  are  anoma- 
lous, because  they  closely  resemble  the  teeth  of 
different  orders  of  mammals,  while  preserving 
tooth  characters  of  reptiles  and  fishes.  Nor  is 
this  resemblance  to  mammals  limited  to  the 
teeth.  It  is  seen  in  almost  every  part  of  the 
skeleton  ;  and  although  there  is  no  actual  transi- 
tion to  mammals,  isolated  parts  of  the  skeletons 
have  been  described  as  mammalian  by  different 
naturalists. 

The  Anomodont  group  is  most  widely  devel- 
oped in  the  Permian  rocks  of  South  Africa.  It  is 
well  represented  in  the  Permian  of  Texas,  and 
other  parts  of  North  America.  It  is  recorded  from 
the  Gondwana  rocks  of  India,  and  from  the  Per- 
mian rocks  of  Orenburg  in  Russia.  Anomodont 
reptiles  have  also  been  found  in  the  red  sandstones 
of  Elgin.  Those  rocks  were  formerly  classed  as 
Old  Red  Sandstone,  and  subsequently  as  Trias 
owing  to  the  affinities  of  their  fossil  reptiles,  but 
on  such  evidence  they  may  be  Permian. 

The  Theriodont  type  generally  possesses  the 
three  kinds  of  teeth  which  characterise  mammals. 
The  canine  teeth  are  strongly  developed.  This 
is  seen  in  the  Russian  genus  Deuterosaurus,  and  in 
the  South  African  genus  Lycosaurus,  both  of  which 
have  the  teeth  in  the  front  of  the  mouth  larger 
than  the  sharp-pointed  representatives  of  the 
grinder  series  placed  at  the  sides.  Deuterosaurus 
finds  its  place  between  the  Theriodonts  and  Pareia- 
saurus.  Some  of  the  South  African  Theriodonts 
have  the  molar  or  grinder  teeth  compressed  and 


PERMIAN. 


119 


II 


OQ.S 


•a  g 


120        THE  STORY  OF  THE  EARTH. 

notched  like  those  of  dogs,  seals,  and  other  car- 
nivorous mammals.  There  are  also  types  which 
have  tuberculate  crowns  to  the  grinders  adapted 
for  crushing  food,  during  which  process  the  crowns 
become  ground  down,  as  among  Insectivora  and 
Rodents. 

There  are  in  the  genus  Dicynodon  only  two  teeth 
in  the  upper  jaw,  which  correspond  to  the  tusks  of 
the  walrus. 

In  Pareiasaurus  the  surface  of  the  skull  is  cov- 
ered with  an  arrangement  of  bones  which  appears 
to  be  identical  with  that  seen  in  the  Labyrintho- 
donts.  Labyrinthodonts  were  formerly  grouped 
with  the  Amphibia,  but  may  be  closely  related  to 
the  Anomodonts.  Pareiasaurus  appear  to  be  in 
many  ways  transitional  between  existing  reptilia 
and  mammalia;  in  so  far  as  can  be  judged  from 
the  skeleton.  It  is  with  existing  marsupials  and 
carnivora,  and  hoofed  or  ungulate  mammals  that 
the  resemblances  in  the  forms  of  the  bones  appear 
to  be  closest. 

The  Trias. 

A  glance  at  a  geological  map  of  England  and 
Wales  shows  that  the  Trias,  which  extends  to  the 
south  of  the  Pennine  chain,  between  Nottingham 
and  the  North  Staffordshire  coal-field,  rests  un- 
conformably  upon  the  denuded  edges  of  the  Per- 
mian and  Carboniferous  strata.  Great  changes 
had  taken  place  in  the  earth's  surface  after  th& 
deposition  of  the  Permian  rocks,  and  a  commence- 
ment was  made  in  the  definition  and  uplifting  ol 
the  Pennine  chain  before  the  Trias  was  laid  down 
against  its  southern  termination. 

In  England  the  Trias  comprises  two  series  of 
sandstones.  The  lower,  named  Bunter,  consists 


THE  TRIAS.  121 

of  conglomerates  and  sands,  which  are  usually 
white,  but  sometimes  red.  There  are  some  evi- 
dences that  its  upper  beds  were  denuded  before 
the  overlying  alternations  of  marls  and  sandstones, 
named  the  Keuper  beds,  were  deposited.  These 
divisions  are  regarded  as  corresponding  to  the 
upper  and  lower  divisions  of  the  Trias  in  Germany, 
between  which  the  shell  limestone,  termed  Muschel- 
kalk,  occurs,  yielding  numerous  marine  fossils, 
and  many  peculiar  fossil  reptiles. 

These  beds  attain  a  thickness  in  Lancashire 
and  Cheshire  of  5200  feet.  The  Keuper  is  there 
twice  as  thick  as  the  Bunter  ;  but  in  Leicester  and 
Warwickshire  the  aggregate  thickness  of  both  di- 
visions of  the  Trias  is  less  than  1000  feet ;  and  of 
that  the  Bunter  forms  about  one-tenth. 

There  is  a  southern  thickening  of  the  Trias  in 
Somersetshire  and  Devon,  where  the  red  rocks 
are  well  exposed  on  the  coast,  and  are  about  2500 
feet  thick.  There  are  few  or  no  fossils  in  the 
Bunter. 

The  rock-salt  of  Cheshire  occurs  chiefly  in  the 
Keuper  marl  in  two  principal  beds,  as  at  North- 
wich,  where  each  of  the  principal  lenticular  masses 
of  salt  is  about  100  feet  thick.  Gypsum  is  also 
found  in  the  marls,  and  is  largely  worked'in  Staf- 
fordshire. The  occurrence  of  the  salt  may  be 
attributed  to  the  evaporation  of  an  inlet  of  the 
sea;  so  that  the  process  was  substantially  the 
same  as  that  now  going  on  in  the  salt-pans  on  the 
shores  of  the  Mediterranean,  where  salt  is  obtained 
artificially  by  evaporation  of  sea-water.  There 
appear  to  have  been  many  of  these  ancient  salt- 
pans. The  lower  bed  at  Northwich  is  about  three- 
quarters  of  a  mile  in  diameter.  The  salt  has  been 
preserved  by  the  marl  in  which  it  is  contained, 


122       THE  STORY  OF  THE  EARTH. 

which  is  impervious  to  water.  The  gypsum  has 
probably  been  formed  out  of  the  carbonate  of 
lime  of  calcareous  organisms,  by  the  action  upon 
them  of  sulphurous  waters,  such  as  result  from 
the  decomposition  of  iron  pyrites,  for  Mr.  Charles 
Darwin  describes  gypsum  as  formed  in  this  way 
in  lakes  on  the  surface  of  South  America. 

In  the  neighbourhood  of  .Storeton,  between 
the  Mersey  and  the  Dee,  an  immense  number  of 
impressions  of  the  feet  of  terrestrial  animals  are 
found,  some  of  which  are  at  present  otherwise 
unknown.  They  may  comprise  the  footprints  of 
Dicynodonts,  of  Rhynchosaurian  reptiles,  and  per- 
haps of  Hyper odapedon,  bones  of  which  occur  in 
Keuper  beds  in  other  parts  of  the  country.  The 
Keuper  at  Warwick  yields  evidences  of  the  skulk 
of  species  of  Labyrinthodon.  And  near  Bristol, 
carnivorous  saurians,  termed  Palaosaurus,  with 
piercing  and  cutting  teeth,  are  found,  which  are 
closely  allied  to  the  great  saurians  of  the  Trias  of 
Wurtemberg,  named  Zandodon. 

The  Stormberg  beds  in  South  Africa  are  prob- 
ably of  Triassic  age,  and  contain  saurians  in  some 
respects  similar  to  those  of  Germany,  such  as 
Massospondylus  and  Euskelesaurus,  and  are  found 
above  the  coal  of  Cape  Colony.  They  all  show 
some  alliance  with  the  Megalosaurus  of  a  later 
age. 

The  saurians  of  the  Muschelkalk  in  Germany 
include  Placodus,  which  has  the  palate  covered 
with  large  flat  crushing  teeth;  and  Nothosaurus, 
which  appear  to  be  intermediate  between  the 
Deuterosaurs  of  the  underlying  Permian  rocks 
of  Russia,  and  the  loiig-necked  Plesiosaurs  of  the 
Oolitic  series  above. 

In  Europe  at  least  the  plants  of  the  coal  period, 


THE   TRIAS.  123 

with  the  exception  of  Calamites,  have  disappeared 
in  the  Trias;  and  various  types  of  Cycads  come 
into  existence,  and  do  not  differ  appreciably  from 
surviving  forms  in  mode  of  growth  and  fruiting. 

The  Oldest  Known  Mammal. 

The  oldest  known  mammal  is  found  in  the 
upper  part  of  the  Trias  or  in  the  Rhsetic  beds. 
There  are  several  species  referred  to  the  genus 
Microlestes.  They  are  only  known  from  isolated 
teeth  and  are  referred  to  mammals  because  the 
roots  of  the  teeth  are  divided.  They  occur  in 
Wurtemberg,  and  at  Frome,  and  Watchet  in 
Somersetshire.  The  great  milk  tooth  from  Watchet 
is  marked  with  seven  ribs,  like  those  on  the  pre- 
molar  tooth  of  the  living  kangaroo-rat  named 
Hypsiprymnus.  The  animal  has  therefore  been  re- 
garded as  a  marsupial  mammal.  Animals  with 
this  type  of  tooth  are  found  in  subsequent  periods 
of  geological  time.  The  lower  jaw  of  a  little 
mammal  named  Plagiaulax  found  in  the  terrestrial 
Purbeck  beds  at  the  close  of  the  Oolites,  has  sim- 
ilar teeth.  This  type  is  repeated  in  the  genus 
Neoplagiaulax,  found  at  Rheims  in  the  lower  ter- 
tiary beds  of  the  Paris  basin.  There  is  therefore 
reason  to  believe  that  very  little  change  has  taken 
place  in  the  oldest  type  of  mammal  since  its  first 
occurrence  in  the  Trias;  and  that  it  was  essen- 
tially a  Kangaroo-rat. 

Peculiar  marine  fossils  appear  in  the  Muschel- 
kalk.  One  of  these  is  the  Cephalopod  shell  Cera- 
tites,  which  is  exactly  intermediate  between  the 
Carboniferous  Goniatites  which  has  the  septa  angu- 
larly folded  and  the  newer  Ammonites  which  has 
the  folds  of  the  septa  digitated  on  both  the  front 


124  THE   STORY   OF   THE   EARTH. 

and  back  margins.  Subsequently,  in  the  Austrian 
Alps,  especially  at  Hallstadt  on  the  north,  and  St. 
Cassian  on  the  south,  the  Upper  Trias  abounds  in 
shells  which  are  a  remarkable  mixture  of  those 
which  survive  from  the  Primary  period,  such  as 
Orthoceras,  Goniatites,  Euomphalus,  Murchisonia, 
with  the  shells  which  are  found  in  the  overlying 
strata,  such  as  Ammonites,  Belemnites,  Nerinoea, 
Trigonia,  Cardita,  Thecidium.  Therefore  the  sepa- 
ration in  life  between  the  Trias  and  the  Permian, 
although  most  marked,  is  not  so  absolute  as  it 
would  have  appeared  to  be  if  those  Alpine  deposits 
had  been  unknown.  And  the  occurrence  of  genera 
which  had  characterised  the  primary  strata,  is  the 
more  interesting  because  other  examples  occur  of 
similar  survival  of  types  of  life  from  the  primary 
time,  in  the  occurrence  of  the  genus  Leptaena  in 
the  Lias,  and  of  Spirifera  in  the  Lias  and  Lower 
Oolites.  Such  occurrences  prove  that  the  change 
in  life  was  a  local  change,  and  that  the  primary 
types  became  extinct  gradually. 

Newer  than  the  Keuper  is  a  series  of  beds  in 
the  west  of  England  not  more  than  100  feet  thick, 
known  as  the  Penarth  beds  or  Rhaetic  beds,  from 
their  great  development  in  the  Rhaetic  Alps.  They 
are  included  in  the  Trias  by  many  writers.  William 
Smith  referred  to  them  as  the  White  Lias,  which 
is  a  compact  limestone  forming  the  top  of  the 
Rhaetic  series,  in  marked  contrast  to  the  Blue  Lias 
above.  The  White  Lias  has  occasionally  been 
used  as  a  substitute  for  lithographic  slate,  which 
it  resembles  in  appearance.  Dragon-flies,  Cock- 
roaches, Grasshoppers,  and  other  insects  are  pre- 
served in  the  White  Lias. 

Fossils  are  plentiful  in  the  underlying  black 
shales,  at  the  base  of  which  is  the  Rhaetic  bone 


THE   LIAS.  125 

bed,  full  of  the  remains  of  fishes  and  reptiles.  Be- 
neath the  black  shale  are  the  tea-green  marls, 
which  pass  down  through  other  marls  into  the 
Keuper  beds.  Species  of  the  existing  Australian 
fish  Ceratodus  evidenced  by  teeth  here  occur  ;  as- 
sociated with  extinct  genera  of  sharks,  such  as 
Hybodus  and  Acrodus  which  characterise  the 
Oolites. 

The  common  sea-shells  of  Rhaetic  age  include 
a  Cockle  and  a  Pecten,  such  as  might  occur  on 
our  own  shores  at  the  present  day,  associated  with 
a  species  of  Avicula,  a  horse-mussel  and  an  oyster. 
At  least  one  large  terrestrial  Saurian  with  teeth 
like  Megalosaurus  occurs  in  Rhaetic  beds  in  Somer- 
set. The  Ichthyosaurs  and  Plesiosaurs,  which 
are  found  for  the  first  time  in  this  stratum  in  this 
country,  do  not  differ  from  those  of  the  newer 
beds. 

Rhaetic  strata  occur  in  most  European  coun- 
tries in  which  the  Trias  is  developed ;  but  are  no- 
where more  grandly  exhibited  than  in  the  Rhaetic 
Alps  of  Lombardy  and  Austria. 


CHAPTER   XV. 

THE    LIAS. 

IN  the  Jura  range  between  France  and  Switz- 
erland, which  furnishes  the  continental  type  for 
rocks  like  our  Lias  and  Oolites,  the  Jurassic  beds 
are  commonly  divided  into  three  parts,  named 
Black,  Brown  and  White.  The  Black  Jura  corre- 
sponds generally  with  the  Lias;  the  Brown  Jura 
with  the  lower  Oolites;  and  the  White  Jura  with 


126 


THE  STORY  OF  THE  EARTH. 


the  upper  Oolites  of  England.  These  three  divi- 
sions in  this  country  are  greatly  subdivided  by 

differences  in  min- 
eral character,  as 
well  as  by  fossils. 

The  Lias  is  gen- 
erally recognised 
by  the  great 
breadth  of  country 
that  it  covers  be- 
tween Whitby  and 
Lyme  Regis,  by 
its  thickness,  and 
its  many  sub-divis- 

MAP  OF  AN  OUTLIER.  ions      which       are 

FIG.  19.— Map  of  an  outlier  of  Lias  be-    traced  through  the 
tween  Market  Drayton  and  Whit- 

church,  proving  that  the   Lias  was     Country.         t    IS,  as 
spread  over  the  West  of  England.       a  rule,  ablue-black 

clay        alternating 

with  thin,  regular  layers  of  earthy  limestone,  so 
that  the  alternations  of  clay  and  limestone  which 
characterise  the  Rhaetic  beds  are  continued,  with 
a  multitude  of  repetitions.  The  Lias  limestones 
have  sometimes  a  tendency  to  be  brown.  The 
thickness  of  the  Lower  Lias  varies  between  500 
feet  at  Lyme  Regis  and  800  feet  on  the  Yorkshire 
coast.  The  common  Lias  Oyster  is  the  Gryphaea 
incurva.  Occasionally,  in  the  country  towards 
Frome  the  Lias  almost  thins  away  where  it  rests 
against  the  Carboniferous  limestone,  and  it  is 
probable  that  the  different  beds  vary  in  thickness 
locally.  The  marine  and  terrestrial  saurians  are 
found  chiefly  in  the  lower  beds  of  the  Lower  Lias, 
in  the  south  of  England.  They  include  both 
Ichthyosaurs  and  Plesiosaurs.  Nearer  the  top 
of  the  Lower  Lias  Scelidosaurus,  a  terrestrial  ar- 


THE   LIAS. 


127 


FIG.  20. — Gryphaea  incurva :  Lias. 


moured  saurian  is  found,  which  in  many  ways  re- 
sembles the  Iguanodon  of  a  later  period,  and  is 
the  type  of  a 
family  with  ver- 
tically serrated 
teeth  named 
Scelidosauridae. 

The  fossils 
which  are  most 
abundant  are  a 
multitude  of  ex- 
tinct species  of 
Ammonites  and 
BeJemnites,  to- 
gether with  an 
oyster  with  an 
involute  mode  of  growth,  known  as  the  genus 
Gryphcea  incurva,  the  devil's  toe-nail  of  the  Dogger 
fishermen.  But  with  such  exceptions  the  great 
multitude  of  the  fossils  belong  to  existing  gene- 
ra. Among  which  are  the  bivalves  Lima,  Pecteny 
Pinna,  Pholadomya,  Astarte,  Avicula,  Modiola,  Tri- 
gonia,  Plicatula ;  and  the  Univalve  shells  Litto- 
rina  and  Pleurotomaria  are  abundant.  Species  of 
the  genus  Ammonites  give  names  to  sub-dfvisions 
or  zones  of  the  Lias.  Some  genera  such  as  Car- 
dinia  and  Hippopodium  are  only  found  in  the  Lias. 

There  is  perhaps  no  sharp  separation  to  be 
drawn  between  the  Lower  and  Middle  Lias.  The 
two  beds  are  conformable  to  each  other,  although 
the  fossils  distinguish  them,  and  there  is  some 
difference  in  their  mineral  character.  The  Mid- 
dle Lias  comprises  the  marl  stone,  which  forms 
an  escarpment  in  the  middle  of  England ;  and  it 
also  includes  the  ironstone  series,  which  is  well 
developed  in  the  Cleveland  district  of  Yorkshire, 


128       THE  STORY  OF  THE  EARTH. 

and  southward  through  Lincolnshire  into  Oxford- 
shire. The  Middle  Lias  is  about  250  feet  thick 
on  the  south  coast ;  and  140  feet  thick  on  the 
Yorkshire  coast.  Near  Cheltenham  the  lower 
part  includes  some  grey  sand,  and  is  about  150 
feet  thick.  The  difference  from  the  Lower  Lias 
in  fossils  is  chiefly  in  the  species  of  Ammonites 

and  Belemnites.  Some 
of  its  upper  beds  are 
known  as  the  Belem- 
nite  beds,  from  the 
abundance  of  this  fos- 
sil. In  these  beds 
many  star  fishes  of 
the  genus  Ophioderma 
are  found,  both  on 
FIG.  2i.— Cardinia  Lister! :  Lias.  the  Yorkshire  coast, 

and  near  Charmouth. 

The  Upper  Lias  is  usually  very  thin  on  the 
coast  of  Dorsetshire,  about  70  feet,  including  the 
associated  sands  near  Charmouth.  But  it  thick- 
ens northward  to  300  feet  near  Cheltenham,  and 
400  feet  further  north  in  Bredon  Hill ;  maintain- 
ing a  thickness  of  300  feet  in  Leicestershire,  but 
thinning  in  Lincolnshire  and  Yorkshire  to  200 
feet  or  less.  On  the  Yorkshire  coast  it  is  often 
known  as  alum  shale,  alum  having  formerly  been 
obtai'ied  from  the  cliffs  and  manufactured  from 
the  shale.  Near  the  base  there  are  beds  of  jet, 
in  which  the  rings  of  growth  of  the  coniferous 
trees  out  of  which  it  was  formed,  may  occasion- 
ally be  observed.  In  the  Upper  Lias  at  Ilminster 
many  Ichthyosaurs,  Plesiosaurs,  and  crocodiles  of 
the  group  Teleosauria  are  met  with.  A  little 
higher  up,  in  the  zone  of  the  Ammonites  communis 
and  Ammonites  bifrons  near  Whitby,  the  same 


THE   LIAS.  129 

genera  occur,  though  they  are  sometimes  met 
with  in  the  underlying  zone  of  Ammonites  serpen- 
tinus,  which  yields  the  jet. 

The  Upper  Lias  of  Gloucestershire  and  War- 
wickshire contains  a  considerable  number  of  in- 
sect remains,  probably  derived  from  the  forests 
in  which  the  coniferous  trees  grew,  which  appear 
to  have  been  allied  to  the  living  Araucaria. 
There  are  also  the  remains  of  Cycads,  such  as 
Zamia,  and  of  a  few  ferns;  so  that,  although 
there  is  no  such  evidence  of  a  land  surface  as  in 
the  Triassic  period,  the  occurrence  of  insects  in 
districts  which,  in  the  previous  period  of  the 
Trias,  yield  the  remains  of  terrestrial  animals, 
appears  to  show  that  the  physical  change  which 
brought  the  Lias  to  an  end,  and  caused  the  Mid- 
ford  sands  to  be  superimposed  upon  it,  was 
substantially  a  bringing  back  again  in  part,  by 
means  of  upheaval,  of  the  shallow  water  condi- 
tions which  prevailed  in  the  Trias  period.  - 

The  yellow  sands,  200  feet  in  thickness  at 
Bridport,  which  pass  northward  into  Somerset- 
shire and  Gloucestershire,  under  the  name  of 
Midford  sands,  gradually  thin  away.  But  since 
they  indicate  the  same  conditions  as  Afterwards 
reappear  in  the  Northampton  sands  in  the  mid- 
dle of  England,  they  may  be  grouped  with  the 
Oolites  rather  than  with  the  Lias. 


130  THE   STORY  OF  THE  EARTH. 

CHAPTER   XVI. 

THE    OOLITES. 

THE  Oolites  are  granular  limestones  of  limited 
extent,  contained  between  clays,  which  in  Great 
Britain  range  between  Dorsetshire  and  the  north 
coast  of  Yorkshire.  They  form  three  limestone 
terraces  in  the  south  of  England,  each  of  which 
rests  on  a  clay,  and  hence  have  sometimes  been 
named  Lower,  Middle,  and  Upper.  It  is  more 
convenient  to  adopt  two  divisions.  The  Lower 
Oolites  include  every  bed  above  the  Lias  to  the 
Cornbrash.  The  Upper  Oolites  extend  from  the 
Oxford  Clay  to  the  Portland  Oolite. 

Lower  Oolites. 

The  Midford  Sands  are  seen  near  Bath  making 
the  base  of  the  Oolites.  The  sand  appears  to  have 
been  derived  from  the  south,  because  the  whole 
of  the  Lower  Oolites  are  represented  by  sands  in 
Dorsetshire.  The  Midford  Sands  disappear  to 
the  north  of  the  Cotswold  Hills,  probably  because 
they  are  represented  there  by  clay  which  is  not 
distinguished  from  the  Lias. 

The  beds  named  Northampton  Sands  occur  in 
the  same  geological  position  in  Northampton- 
shire. They  are  about  70  feet  of  brown  sands 
and  yellow  sandstone,  with  ironstone,  which  is  a 
valuable  iron  ore.  They  are  capped  by  grey  and 
white  sand,  containing  beds  of  lignite,  which  may 
have  accumulated  in  an  estuary.  Their  fossils 
are  mainly  those  of  the  Inferior  Oolite;  and  they 
are  probably  a  geographical  continuation  of  the 
Midford  Sands. 


THE  OOLITES. 


IJl 


132        THE  STORY  OF  THE  EARTH. 

In  Yorkshire  the  beds  which  rest  on  the  Lias 
are  known  as  Dogger.  They  are  about  90  feet 
of  yellow  sand  covered  by  concretions  of  Oolitic 
ironstone,  usually  sandy.  Like  the  Northampton 
sands,  they  are  capped  by  current-bedded  sands 
and  shales  among  which  are  beds  of  impure  coal. 
The  fossils  of  those  estuarine  sands  include  ferns, 
a  large  Equisetum  often  found  erect  among  the 
blown  sand,  and  the  Cycad  Zamia.  They  indi- 
cate an  old  land  surface.  The  beds  which  rest 
upon  these  sands  show  a  similar  want  of  conti- 
nuity where  they  are  exposed  at  the  surface  of 
the  country. 

The  Inferior  Oolite  is  limited  to  the  west  of 
England.  In  the  Cotswold  Hills  it  is  about  250 
feet  thick,  mainly  limestone.  At  its  base  is  the 
pea  grit,  with  concretions  about  the  size  of  peas. 
Above  it  are  the  Oolite  limestones  with  texture 
like  the  hard  roe  of  fish,  known  to  builders  as 
freestone,  termed  Roe-stone,  which  alternate  with 
marl.  A  little  sand  remains  when  the  limestone 
is  dissolved.  The  rock  thins  away  to  the  east 
beyond  Woodstock.  Its  fossils  include  Terebra- 
tula  fimbrta,  Pholadomya  fidicula,  Ostrea  Marshii, 
Clypeus  plotii. 

In  Northamptonshire  the  beds  are  replaced, 
first,  at  the  base  by  a  thin  bedded,  shelly  lime- 
stone used  for  roofing,  known  as  Collyweston 
Slate.  It  is  sometimes  20  feet  thick.  The  great 
mass  of  the  Inferior  Oolite  is  represented  by  a 
limestone  known  as  Lincolnshire  limestone,  which 
thins  away  to  the  north  and  south.  It  is  200 
feet  thick  at  its  maximum,  and  forms  an  escarp- 
ment terrace  in  Northamptonshire  .and  Lincoln- 
shire. 

In   Yorkshire   this   period   of  time   is   repre- 


THE   OOLITES.  133 

sented  by  the  middle  estuarine  beds  with  bands 
of  coal  and  plants,  seen  in  Gristhorpe  Bay; 
above  which  is  the  marine  Scarborough  lime- 
stone, with  the  Inferior  Oolite  fossil  Ammonites 
Humphrey  sianus. 

The  Fuller's  Earth  in  the  south  of  England 
caps  the  Inferior  Oolite,  and  divides  it  from  the 
great  Oolite.  It  is  a  series  of  clays,  marl,  and 
earthy  limestone  known  as  Fuller's  Earth  rock. 
The  stratum,  sometimes  blue,  sometimes  yellow 
of  Fuller's  Earth  of  commerce  is  only  a  few 
feet  thick.  The  Fuller's  Earth  in  Dorsetshire  is 
estimated  at  400  feet  in  thickness.  In  the  Mid- 
land counties  the  Upper  Estuarine  beds  represent 
it  with  30  feet  of  sands,  clays  and  limestones.  -  On 
the  Scarborough  coast  their  thickness  is  200  feet, 
and,  besides  remains  of  terrestrial  plants,  they 
contain  the  fresh  water  pond  shell  Anodonta. 

The  Great  Oolite  is  more  local  than  the  Infe- 
rior Oolite.  At  Minchinhampton  it  includes 
shelly  beds.  At  Bath  it  is  a  freestone  50  feet 
thick,  sometimes  with  oolitic  texture,  sometimes 
marly.  It  is  seldom  oolitic  to  the  north  of  the 
Cotswold  Hills. 

To  the  north-east,  the  Bath  oolite 'is  repre- 
sented by  the  Stonesfield  slate,  a  concretionary 
thin-bedded  limestone,  formed  in  part  by  the  de- 
struction of  older  beds  of  oolitic  rock.  It  indi- 
cates near  proximity  to  land.  Its  fossils  are  the 
fronds  of  ferns,  foliage  and  fruits  of  cycads, 
branches  of  coniferous  trees.  There  are  beetles, 
dragon-flies,  butterflies,  and  other  insects.  Lower 
jaws  of  four  kinds  of  mammals  have  been  found, 
named  Amp  hither  ium,  Amphilestes,  Phascolotherium, 
and  Stereognathus^  which,  on  the  evidence  of  their 
teeth,  appear  to  be  allied  to  Marsupials,  though  a 


134        THE  STORY  OF  THE  EARTH. 

thigh  bone  resembles  that  of  the  Australian  duck 
bill  Ornithorhynchus.  Flying  saurians  are  named 
Rhamphocephalus.  Long  snouted  types  of  croco- 
dile occur,  and  remains  of  the  great  terrestrial 
carnivorous  Megalosaurus,  which  appeared  first 
in  the  Inferior  Oolite.  All  these  fossils  are  in  a 
bed  full  of  marine  shells. 

About  Bath  and  in  Dorsetshire  the  Great 
Oolite  is  succeeded  by  a  brown  clay  crowded 
with  the  Apiocrinus,  or  pear  encrinite,  which  has 
a  cylindrical  stem.  This  clay,  named  Bradford 
clay,  separates  the  Great  Oolite  from  the  thin- 
bedded  Forest  marble  above  it.  That  shelly  lime- 
stone at  Enslow  Bridge  near  Oxford,  at  Chipping 
Norton,  and  other  localities  yields  the  remains  of 
Cetiosaurus,  which  is  the  largest  terrestrial  fossil 
reptile  found  in  England. 

In  Northamptonshire  and  Lincolnshire  there 
is  a  clay  above  the  Great  Oolite  limestone,  in  the 
position  of  the  Forest  marble  and  Bradford  clay, 
called  the  Blisworth  clay. 

All  these  irregularities  in  mineral  character  of 
the  Lower  Oolites  as  they  are  traced  through 
England  may  result  from  the  sinuous  contours 
of  bays  and  promontories  of  the  shores  at  the 
time  of  their  depositure,  which  did  not  corre- 
spond with  the  line  along  which  the  several  de- 
posits come  to  the  surface  of  the  country  at  the 
present  day. 

Cornbrash  is  the  name  given  to  a  shelly  lime- 
stone which  closes  the  Lower  Oolitic  period.  It 
is  rarely  more  than  10  to  15  feet  thick.  Many  of 
its  fossils  are  like  those  of  the  Inferior  Oolite. 
The  most  characteristic  species  is  the  Avicula 
echinata.  It  is  the  first  deposit  since  the  Lias 
which  extends  continuously  through  England, 


THE   OOLITES.  135 

and  is  seen  between  Scarborough  and  Weymouth. 
It  is  evidence  of  a  change  in  the  tilt  of  the  sea- 
bed, which  makes  a  break  in  the  succession  of 
the  strata. 

Upper  Oolites. 

There  is  no  break  in  the  order  of  succession 
of  the  Oolitic  rocks  above  the  Cornbrash,  which 
would  divide  them  into  Middle  and  Upper  Oolites. 
The  differences  in  mineral  character  between  the 
several  beds  are  such  as  may  be  attributed  to 
changes  in  level  of  the  old  land  from  which  the 
sediments  were  derived,  which  removed  the  source 
of  the  deposited  material  from  time  to  time,  to 
greater  distances. 

The  first  effect  of  such  an  upheaval  is  seen 
in  the  Kelloway  Rock,  which  forms  concretionary 
sandy  beds,  and  yellow  sands  and  limestones  80 
feet  thick  on  the  Yorkshire  coast.  It  is  said  to 
occur  in  Bedfordshire.  It  is  named  from  occur- 
rence at  Kelloway  Bridge  in  Wiltshire.  This  dis- 
tribution may  be  connected  with  proximity  to  the 
Mendip  ridge  in  the  latter  case,  and  connected 
with  the  Pennine  chain  in  the  former.  The  con- 
ditions which  produced  the  Stonefield  slate  prob- 
ably produced  the  Wiltshire  Kelloway  rock ;  and 
the  conditions  of  the  sand  beds  in  the  Yorkshire 
Lower  Oolites  are  approximated  to  by  the  York- 
shire Kelloway  rock.  This  deposit  is  more  im- 
portant in  France. 

The  Oxford  day  is  manifestly  the  consequence 
of  a  depression  which  prevented  the  coarse  sandy 
sediment  from  reaching  so  far  out  from  its  source 
as  in  the  previous  age.  This  clay,  which  is  170 
feet  thick  in  Yorkshire,  and  600  feet  thick  in 
Dorset,  is  therefore  superimposed  upon  the 


136       THE  STORY  OF  THE  EARTH. 

Kelloway  rock.  Near  its  base,  about  Peter- 
borough, the  Oxford  clay  abounds  in  remains  of 
timber  trees,  apparently  coniferous.  Its  plant 
remains  also  include  Cycads.  It  yields  the  ter- 
restrial reptiles  Cetiosaurus  and  Omosaurus,  with 
Teleosaurian  crocodiles,  Ophthalmosaurus,  which 
is  an  Ichthyosaur  with  three  bones  in  the  fore- 
arm instead  of  two.  The  big  headed  Pliosaurus 
is  common;  Muraenosaurus  is  a  long-necked  plio- 
siosaurian  with  single  headed  ribs  to  the  neck, 
and  two  bones  in  the  forearm.  The  common 
shells  in  the  Oxford  clay  are  the  oyster  Gryphcea 
dilatata,  Belemnites  hastatus,  Ammonites  Duncani, 
and  Ammonites  cordatus.  The  Ampthill  Clay  and 
Oxford  Oolite  rest  upon  the  Oxford  clay.  The 
Ampthill  clay  is  seen  between  Ampthill  in  Bed- 
fordshire and  Acklam  Wold  in  Yorkshire. 

The  Coralline  Oolite  interlaces  with  the  clay 
in  Bedfordshire  by  a  number  of  thin  beds  of  blue 


FlG.  23. — Belemnites  Oweni,  an  internal  shell  of  a  kind  of  cuttle- 
fish. The  "Guard"  is  broken  to  show  the  conical  phragma- 
cone  which  penetrates  into  it.  Oxford  Clay. 

earthy  limestone.  Traced  southward  by  Shot- 
over,  it  forms  two  divisions;  and  at  Weymouth 
there  is  the  sandy  lower  calcareous  grit  well  de- 
fined, and  an  upper  grit  or  sand  which  passes  up 
to  the  Kimeridge  clay.  In  Yorkshire  this  Oolite 
extends  through  the  Howardian  Hills  by  Malton, 
through  the  Vale  of  Pickering  to  Filey.  At  Up- 
ware,  on  the  river  Cam,  a  small  reef  full  of  corals 
appears  to  result  from  the  Carboniferous  lime- 
stone having  furnished  calcareous  matter  to  the 


THE  OOLITES.  137 

neighbouring  sea.  The  reptiles  of  this  age,  Omo- 
saurus  and  Pliosaurus,  are  like  those  of  the  Oxford 
clay,  but  a  great  Megalosaurian,  named  Strepto- 
spondylus,  has  also  been  found  at  Weymouth  and 
Malton  in  Yorkshire. 

The  Kimeridge  Clay. — The  reef  of  limestone  at 
Upware  appears  to  be  a  dividing  point  for  the 
Kimeridge  clay,  which  comes  next  in  vertical  suc- 
cession. In  Cambridgeshire  it  is  about  40  feet 
thick,  but  thickens  south-west  to  Dorsetshire  to 
more  than  600  feet  thick,  and  its  northern  thick- 
ening to  Yorkshire  is  almost  as  great.  This  clay 
contains  inflammable  beds  known  as  Kimeridge 
coal,  which  divide  into  thin  sheets  like  paper,  and 
are  full  of  marine  fossils.  In  Dorsetshire  the  clay 
is  used  as  fuel,  and  has  been  used  in  making 
paraffin  candles,  and  to  produce  gas  for  illumina- 


FIG.  24. — Section  showing  the  succession  of  strata  east  of  Oxford. 

tion  of  the  neighbouring  villages.  These  clays 
are  full  of  beds  of  concretions  of  earthy  lime- 
stone, named  septaria,  which  are  each  2  or  3  feet 
in  diameter. 

The  oldest  known  representative  of  the  Iguan- 
odon  is  found  in  this  clay  at  Cumnor.  And  be- 
tween Ely  in  Cambridgeshire  and  Swindon  many 
fossil  reptiles  are  found,  such  as  Teleosaurian 
crocodiles,  peculiar  turtles  and  Ichthyosaurs. 
Colymbosaurus  is  a  long  necked  Plesiosaur  with 
single  heads  to  the  neck  ribs,  distinguished  by  the 
massiveness  of  its  arm  bones,  and  by  having  three 


138       THE  STORY  OF  THE  EARTH. 

bones  in  the  forearm  instead  of  two.  Omosaurus 
is  a  large  land  saurian  found  at  Swindon.  The 
common  shells  of  the  clay  include  Ostrea  delto  deay 
Exogyra  virgula,  Lingula  ovalis  and  Ammonites 
biplex. 

The  Solenhofen  slate  of  Bavaria  makes  known 
numerous  insects  and  other  forms  of  terrestrial 
life  of  this  period,  including  the  oldest  known  bird. 

The  Oldest  Known  Bird. 

A  bird  is  known  by  its  feathers ;  though  there 
is  no  reason  why  the  covering  to  the  skin  should 
not  be  as  variable  in  this  group  of  animals  as 
among  reptiles  or  mammals.  It  is  therefore  re- 
markable that  the  oldest  known  bird  named 
Archczopteryx  has  feathers  as  well  developed  as  in 
the  existing  representatives  of  the  class  and  simi- 
larly arranged.  It  is  found  in  the  lithographic 
slate  of  Solenhofen  in  Bavaria,  which  is  of  about 
the  age  of  the  Kimeridge  clay,  in  the  Upper  part 
of  the  Oolites.  The  animal  is  an  elegant  slender 
bird  which  is  chiefly  remarkable  for  showing  teeth 
in  the  jaws.  About  twelve,  short  and  conical,  oc- 
cur on  each  side  in  the  upper  jaw.  The  skull  is 
about  two  inches  long,  shaped  like  the  skull  in 
many  existing  birds,  with  a  circle  of  sclerotic  bones 
defending  the  eye. 

The  neck  and  back  are  each  about  2f  inches 
long,  and  there  is  a  slender  rat-like  tail,  of  more 
than  twenty  elongated  vertebrae,  which  is  6-j-  inches 
long.  The  fore  limbs  are  as  well  developed  as  the 
hind  limbs.  But  they  differ  from  existing  birds  in 
the  bones  of  the  metacarpus  not  being  blended 
together,  and  in  the  three  digits  terminating  in 
sharp  claws.  The  number  of  the  phalanges  in  the 


THE   OOLITES. 


139 


three  fingers  is  2,  3,  4.     They  are  thus  similar  to 
the  digits  of  the  hind  limb,  and  are  apparently 


*          s 


FIG.  25.  — Skeleton  of  the  oldest-known  bird,  Archczofiteryx  macru- 
ra,  showing  impressions  of  the  feathers  on  the  wings,  legs,  and 
tail.  From  the  lithographic  stone  of  Solenhofen  (after  Dames). 

capable  of  being  applied  to  the  ground  like  the 
fore  limbs  of  a  quadruped,  although  the  great 
development  of  the  feathers  attached  to  the 
arm  bones  demonstrates  that  the  wings  were 


140       THE  STORY  OF  THE  EARTH. 

constructed   on    the    same   plan   as   in   existing 
birds. 

The  femur  or  thigh  bone  is  about  two  inches 
long;  the  drum  stick  is  more  than  two  inches  and 
a  half.  And  the  slender  metatarsus  is  about  an 
inch  and  a  quarter  long.  The  three  points  of  dif- 


FIG.  26.— Skull  of  the  oldest-known  bird  with  teeth.  Archae- 
opteryx  macrura  (after  W.  Dames).  A.  orbit  cf  the  eye.  B. 
pre-orbital  vacuity.  C.  nostril.  Scl.  circle  of  bony  plates 
round  the  eye.  h.  tongue  bones,  mi.  lower  jaw.  m  and  tm. 
jaw  bones.  /.  tear-bone,  n.  nose-bone.  (After  Dames.) 

ference  from  existing  birds  are,  the  elongated  tail 
bearing  feathers  on  each  vertebra,  the  teeth,  and 
the  claws  on  the  three  digits  of  the  hand. 


Close  of  the  Oolitic  period. 

A  great  change  in  life  took  place  between  the 
Kimeridge  clay  and  the  Portland  Oolite  which 
rests  upon  it.  And  although  the  granular  Oolitic 


THE  OOLITES.  141 

texture,  which  the  Portland  limestone  shows  in 
the  south  of  England,  has  caused  it  to  be  asso- 
ciated with  the  older  Coralline  Oolite,  and  Lower 
Oolites,  it  yet  marks  the  beginning  of  a  great  up- 
rising of  the  sea-bed,  which  extended  eastward 
from  the  Mendip  Hills  during  the  succeeding 
periods  of  time.  Many  of  its  fossils  may  justify 
its  position  in  the  Oolitic  series,  but  the  physical 
conditions  of  upheaval,  and  representation  by 
limestone  and  sand,  appear  also  to  link  it  with  the 
great  terrestrial  epoch  of  Purbeck  and  Wealden 
beds,  which  form  a  portion  of  the  Neocomian 
period  of  time. 

The  Portland  strata  are  almost  limited  in  a 
recognisable  form  to  the  south  of  England, 
though  the  horizon  is  defined  by  fossils  in  the 
clay  beds  at  the  top  of  the  Kimeridge  clay  in 
Filey  Bay.  A  thin  sandy  layer  with  characteristic 
Portland  fossils  caps  the  Kimeridge  clay  through 
Lincolnshire,  Norfolk,  and  Cambridgeshire.  It  is 
not  always  possible  to  draw  a  line  between  this 
feeble  representative  of  the  Portland  sand  and 
the  overlying  sand  termed  Neocomian,  so  that  the 
Portland  sand  appears  like  the  beginning  of  the 
shore  conditions,  which  lasted  in  the  area'of  South 
Britain  till  the  close  of  the  Lower  Greensand. 

On  the  Yorkshire  coast  there  is  no  break 
whatever  in  mineral  character  from  the  Kimer- 
idge clay  to  the  Hunstanton  Red  Limestone  at 
the  base  of  the  chalk. 

Among  the  fossils  of  the  Portland  beds  several 
species  of  Perna,  Astarte,  etc.,  are  found  which  re- 
semble fossils  of  the  Kimeridge  clay,  but  there 
are  also  species  of  Cyprina,  Pecten,  Cerithium,  etc., 
which  resemble  Neocomian  forms.  Lucina  Port- 
landica  is  one  of  the  characteristic  bivalve  fossils. 


142       THE  STORY  OF  THE  EARTH. 

CHAPTER  XVII. 

NEOCOMIAN. 

THE  Neocomian  period  of  geological  time  is 
completely  represented  in  Great  Britain  in  the 
Speeton  clay,  which  is  about  300  feet  thick,  and 
seen  to  the  north  of  Flamborough  Head.  The 
basement  bed  of  this  deposit  is  the  Coprolite 
bed  which  divides  it  from  the  Kimeridge  clay 
on  which  the  Speeton  clay  rests.  That  bed  is  a 
layer  of  nodules  of  phosphate  of  lime,  which  ap- 
parently were  formed  about  fossils,  like  similar 
beds  of  phosphate  of  lime  in  newer  deposits  in 
Bedfordshire  and  Suffolk.  This  layer  of  phos- 
phates marks  a  change  in  the  life;  so  that  the 
shells  which  characterise  the  Kimeridge  clay  be- 
low do  not  pass  above  it.  It  was  formerly  sup- 
posed to  occur  at  the  top  of  the  Portland  beds, 
but  the  Ammonites  regarded  as  Portlandian  oc- 
cur above  this  junction  bed. 

There  is  therefore  some  ground  for  regarding 
the  Speeton  clay  above  the  Coprolite  bed  as 
representing  in  unbroken  marine  sequence  the 
geological  ages  which  in  the  south  of  England 
are  partly  lacustrine,  partly  terrestrial,  and  partly 
marine,  and  known  as  the  Portland  beds,  the  Pur- 
beck,  and  the  Wealden  beds,  and  the  Lower  Green- 
sand. 

The  lowest  division  of  the  Speeton  clay  is 
known  as  the  zone  of  Belemnites  lateralis.  The 
Lucina  Portlandica  is  found  in  the  Coprolite  bed, 
and  a  variety  of  the  Exogyra  sinuata  appears  some- 
what higher  up.  The  next  division  is  the  zone  of 
Belemnites  jaculum,  which  ranges  through  about 


NEOCOMIAN.  143 

120  feet  of  clay  in  which  there  is  a  large  number 
of  characteristic  Ammonites,  with  species  of  Tere- 
bratula  and  Rhynchonella.  The  third  zone  is  that 
of  the  Belemnites  semi-canaliculatus.  In  this  zone 
in  the  Ammonites  Deshayesii  found  in  the  Lower 
Greensand  of  the  south  of  England.  The  upper- 
most zone  of  the  Speeton  clay  is  that  of  Belemnites 
minimus.  This  fossil  which  in  the  south  of  Eng- 
land abounds  in  the  Gault,  here  occurs  in  asso- 
ciation with  Inoceramus  concentricus,  Inoceramus 
sulcatus  and  Nucula  pectinata,  which  are  also  com- 
mon gault  species.  The  clays,  which  are  mostly 
dark  blue,  and  blue  black,  become  red  at  the  top, 
so  that  there  appears  to  be  a  transition  from  the 
red  clay  to  the  argillaceous  red  limestone,  known 
as  the  Hunstanton  Limestone,  or  red  chalk  of 
early  writers. 

The  top  beds  of  the  Speeton  clay  may  there- 
fore be  newer  than  the  Neocomian  of  which  the 
upper  limit  is  the  Lower  Greensand  of  the  south 
of  England.  The  other  beds  give  a  threefold 
division.  So  that  the«Portland  and  Purbeck  lime- 
stones of  Swindon  correspond  to  the  Belemnites 
lateralis  beds,  which  are  represented  by^the  Up- 
per Volga  beds  of  Russia.  The  middle  beds, 
apparently,  would  correspond  to  the  Wealden 
period  of  the  south  of  England,  Belgium,  and 
Hanover,  while  the  zone  of  Belemnites  semi-cana- 
liculatus corresponds  to  the  Lower  Greensand. 

While  these  beds  were  being  laid  down  in  a 
region  which  underwent  but  little  change  of  level, 
so  that  an  uninterrupted  deposit  of  clay  was  ac- 
cumulated, the  land  was  upheaved,  further  south, 
into  those  shallow  water  conditions,  of  which  the 
Portland  beds  are  evidence,  which  pass  without 
an  appreciable  break  into  the  lacustrine  and  ter- 


144        THE  STORY  OF  THE  EARTH. 

restrial  Puibeck  series.  There  is  nothing  to  show 
that  the  terrestrial  surface  was  more  or  less  than 
an  enlargement  of  the  land  which  in  previous  ages 
of  secondary  time  had  supplied  the  insects,  mam- 
mals, plants  and  terrestrial  reptiles  which  are 
found  in  various  beds  of  the  Upper  and  Lower 
Oolites,  and  which,  by  its  varying  elevation, 
had  effected  the  distribution  and  nature  of  the 
sediments,  all  through  the  lower  secondary  pe- 
riod. 

The  limestone  beds  appear  to  have  owed  their 
existence  largely  to  the  influence  of  the  Carbon- 
iferous limestone,  for  many  evidences  are  found 
that  it  was  repeatedly  denuded,  while  the  sand- 
stones and  clays  were  supplied  partly  by  sedi- 
ments derived  from  denudations  of  older  slatey 
and  schistose  rocks.  The  existence  of  the  Pur- 
beck  beds,  which  in  Dorsetshire  are  alternations 
of  thin-bedded  white  limestone,  with  bands  of 
•dark-coloured  clay,  shows  that  the  streams  of 
fresh  water  coming  from  off  the  land  into  the 
lake,  charged  the  fresh  water  with  carbonate  of 
lime,  just  as  they  had  previously  charged  the 
sea;  while  the  uplifting  of  the  earth's  surface 
above  the  sea-level  was  so  gradual  that  there  is 
no  break  between  the  marine  and  fresh  water 
beds.  Near  the  base  of  the  Purbeck  beds  in 
Dorsetshire  an  old  land  surface  is  found,  known 
to  the  quarrymen  as  the  Dirt  Bed.  It  is  well 
seen  in  the  cliffs  of  Lulworth  Cove  in  the  Isle  of 
Purbeck,  and  in  the  Isle  of  Portland.  Here  co- 
niferous trees,  sometimes  a  foot  or  two  in  diame- 
ter, lie  prostrate,  but  the  roots  and  lower  parts 
of  the  trunk  remain  erect  as  they  grew.  Some 
of  the  coniferous  trees  show  nearly  200  rings  of 
annual  growth  and  a  length  of  sixty  feet.  Among 


NEOCOMIAN.  145 

them  are  the  short  stems  of  Cycads,  which  resem- 
ble the  living  Cycas  revoluta. 

The  Lower  Purbeck  also  contains  a  multitude 
of  insect  remains,  on  several  different  horizons. 
They  are  chiefly  in  cream-coloured  marl,  and 
include  the  wing  cases  and  bodies  of  beetles, 
dragon-flies,  and  other  insects. 

A  terrestrial  surface  at  the  base  of  the  Middle 
Purbeck  is  evidenced  by  many  jaws,  and  a  few 
other  remains  of  small  mammals.  They  appear 
to  be  little  insectivorous  marsupials,  such  as 
Triconodon,  Spalacotherium^  and  the  type  like  the 
kangaroo-rat,  which  is  named  Plagiaulax. 

The  Middle  Purbeck  includes  some  marine 
layers  with  cockle  shells,  oysters  and  pectens, 
with  occasional  ripple-marked  sandstone.  The 
marine  beds  alternate  with  the  fresh-water  beds, 
in  which  the  common  shells  which  live  in  exist- 
ing ponds,  Paludina,  Planorbis,  Physa,  etc.,  appear 
for  the  first  time. 

The  Upper  Purbeck  beds  are  interesting,  first, 
for  yielding  the  grey,  Paludina  marble,  anciently 
used  for  decorative  carving  and  monuments  in 
the  interior  of  churches;  and,  secondly,  for  the 
number  of  its  fresh-water  tortoises,  nanred  Pleuro- 
sternon,  which  differ  from  their  living  allies  in 
having  an  extra  pair  of  bones,  stretching  over 
the  middle  of  the  breast-plate,  known  as  the 
plastron. 

In  Swanage  Bay  the  overlying  Wealden  beds 
differ  from  the  Purbeck  beds  in  being  sands  and 
clays.  In  the  boring  near  Battle  in  Sussex,  the 
Purbeck  beds,  formerly  known  as  the  Ashburn- 
ham  beds,  contain  some  important  layers  of  gyp- 
sum, but  no  other  calcareous  deposits ;  and  are 
like  the  Wealden  beds  in  mineral  character. 
10 


146        THE  STORY  OF  THE  EARTH. 

The  Wealden  strata  exhibit  two  types.  In 
Dorsetshire  and  in  the  Isle  of  Wight  they  com- 
prise alternations  of  numerous  beds  of  grit,  sand 
and  clay,  frequently  of  the  most  brilliant  red 
colour.  A  few  marine  shells,  species  of  Pecten, 
occur  in  the  lower  Wealden  beds  of  the  Isle  of 
Purbeck.  In  the  Isle  of  Wight  they  have  yielded 
multitudes  of  vegetable  remains,  among  which 
are  pine  cones,  and  especially  the  fossil  forest  of 
Brook,  where,  however,  the  great  forest  trees  ap- 
pear to  be  drifted  and  water-logged.  In  these 
beds  have  been  found  the  remains  of  many 
extraordinary  terrestrial  reptiles.  The  Ornitho- 
cheirus  type  of  Pterodactyl  appears,  which  has  the 
earlier  joints  of  the  backbone  blended  together, 
as  in  the  frigate  bird.  There  is  a  terrestrial 
saurian  named  Polacanthus,  which  had  the  lower 
part  of  the  body  covered  with  a  complete  shield 
like  that  of  an  armadillo.  Associated  with  it  is 
the  Belgian  Iguanodon,  the  great  Cetiosaurian 
named  Ornithopsis,  and  the  genera  named  Hypsile- 
phodon,  Sphenospondylus,  Vectisaurus,  etc. 

Further  to  the  north,  in  the  typical  Wealden 
country  of  Kent,  Surrey,  and  Sussex,  these  beds, 
instead  of  being  multitudinous  and  irregular,  be- 
come separated  into  great  divisions  of  tolerably 
uniform  mineral  character.  The  Ashdown  Sand 
is  in  the  main  a  hard  yellow  sandstone.  The 
Wadhurst  Clay  above  it  is  a  number  of  alterna- 
tions of  shale  and  hardened  sand  frequently 
ferruginous,  with  plant  remains.  The  Tunbridge 
Wells  Sand  is  about  150  feet  of  sandstone  more 
or  less  divided  by  thin  beds  of  clay,  which  may 
thicken  locally.  Above  these  beds,  which  are 
named  Hastings  Sand,  comes  the  Weald  Clay, 
which  is  900  feet  thick  in  the  south-east  of  Kent, 


NEOCOMIAN.  147 

and  400  feet  thick  in  the  west  of  Surrey.  It  is 
full  of  bands  of  fresh-water  limestone,  formed  of 
fresh-water  shells,  especially  Paludina. 

In  various  localities  in  Sussex,  particularly 
near  Hastings,  the  footprints  of  Iguanodon  have 
been  found,  and  both  there  and  at  Cuckfield  a 
multitude  of  bones  occur.  They  include  small 
species  of  Plesiosaur  of  the  genus  Cimoliosaurus 
and  an  Ichthyosaur  possibly  estuarine,  together 
with  a  group  of  terrestrial  saurians,  entirely  dif- 
ferent from  those  of  the  Isle  of  Wight.  These 
remains  include  Pelorosaurus,  the  Iguanodon  Man- 
telli,  Suchosaurus  and  Megalosaurus,  as  well  as 
fresh-water  tortoises.  Many  plants  are  met  with 
on  this  horizon,  including  some  ferns,  like  Sphe- 
nopteris,  with  the  fronds  well  preserved ;  and  nu- 
merous Cycads.  Fresh-water  shells  include  the 
existing  Unio.  The  terrestrial  fauna  is  very  im- 
perfectly known  in  comparison  with  that  buried 
in  the  deep  valleys  near  Mons  in  Belgium,  from 
which  entire  skeletons  of  Iguanodon  and  other 
reptiles  have  been  obtained.  Along  the  northern 
outcrop  of  the  Neocomian  strata,  by  Farringdon, 
Potton  and  Upware,  numerous  remains  have  oc- 
curred of  Iguanodon,  Megalosaurus,  and  other 
terrestrial  saurians  like  those  of  the  Weald,  and 
with  them  are  remains  of  Cycads,  Pandanus  and 
Pines.  On  this  outcrop  the  Neocomian  Sand 
rests  successively  on  the  Kimeridge  Clay,  Ampthill 
Clay,  and  Oxford  Clay  as  at  Sandy  and  Woburn 
in  Bedfordshire,  showing  that  an  unconformity 
separates  the  Neocomian  strata  from  the  Oolites 
in  the  middle  of  England. 

The  Lower  Greensand  is  a  marine  bed  which 
extends  over  the  fresh-water  series  of  the  Weald. 
But  beyond  the  Wealden  area  the  sands  are 


1^8  THE    STOKY   OF   THE   EARTH. 

termed  Neocomian  ;  because,  although  they  ex- 
hibit a  threefold  division,  it  is  difficult  always  to 
prove  that  these  parts  correspond  to  the  Portland 
and  Purbeck,  Weald,  and  Lower  Greensand  re- 
spectively. In  the  Isle  of  Wight,  the  Lower 
Greensand  consists  of  a  large  number  of  alter- 
nating beds  of  sand  and  clay,  more  than  900  feet 
thick.  More  than  eighty  distinct  layers  have 
been  grouped  into  sixteen  beds.  So  that  the 
'conditions  of  deposition  of  the  Weald  seem  to 
have  continued  through  the  succeeding  epoch  of 
time ;  and  occasionally  the  remains  of  an  Iguan- 
odon  became  floated  into  the  Lower  Greensand 
from  land  diminished  by  depression  of  its  level. 
There  is  the  same  correspondence  of  the  Lower 
Greensand  to  the  Wealden  beds  in  stratigraphical 
succession  in  the  typical  Wealden  area  of  Sussex. 
The  Lower  Greensand  is  divided,  in  the  section 


w. 

FIG.  27. — Section  from  Folkestone  to  Hythe,  showing  above  the 
fresh-water  Weald  Clay,  the  divisions  of  the  marine  Lower 
Greensand,  named  Atherfield  beds,  Hythe  beds,  Sandgate 
beds,  Folkestone  beds. 

between  Hythe  and  Folkestone,  into  the  Ather- 
field Clay  at  the  base,  which  is  sometimes  a  ma- 
rine clay  resting  on  the  Weald  Clay,  and  some- 
times loose  sharp  sand.  Secondly,  the  Hythe 
beds  (or  Kentish  rag)  are  alternations  of  thin 
bedded  limestone  and  sand  with  beds  of  chert. 
Thirdly,  the  Sandgate  beds  are  sandy  clays  not 
very  coherent,  often  green,  like  the  underlying 


LOWER   CRETACEOUS   STRATA.  149 

beds.  And  fourthly,  the  Folkestone  beds  are 
usually  yellowish,  unconsolidated,  and  appear  to 
correspond  to  the  ferruginous  sands  of  Shanklin 
in  the  Isle  of  Wight.  Fuller's  earth  occurs  at 
many  horizons  in  the  Sandgate  beds.  The  Hythe 
beds  occasionally  contain  beds  of  chert,  derived 
from  the  growth  and  breaking  up  of  siliceous 
sponges.  Near  Maidstone  it  has  yielded  boulders 
of  granite,  which  may  have  been  the  anchor  stones 
of  marine  plants  like  Fucus.  Remains  of  terres- 
trial plants  and  of  Iguanodon  indicate  near  prox- 
imity of  the  Maidstone  area  to  land,  which  is 
paralleled  in  the  Isle  of  Wight. 


CHAPTER    XVIII. 

LOWER    CRETACEOUS    STRATA. 

EVER  since  the  Carboniferous  period  the  influ- 
ence of  a  dividing  line  extending  east  to  west,  due 
to  elevation  of  the  rocks  between  Worcestershire 
and  Lincolnshire,  has  been  more  or  less  persistent. 
It  has  influenced  the  mineral  character ,of  strata 
and  distribution  of  life.  It  has  given  a  distinct 
character  to  the  Oolitic  rocks  south  of  Banbury, 
to  that  shown  by  the  succession  of  rocks  further 
north.  The  same  geographical  conditions  separate 
the  Neocomian  rocks  north  and  south  of  the  land 
barrier  indicated  on  the  south  by  the  Purbeck  and 
Wealden  rocks.  A  like  physical  difference  is  seen 
in  some  of  the  Cretaceous  rocks. 

In  so  far  as  can  be  judged  by  fossils,  the  change 
from  Speeton  clay  to  Hunstanton  limestone  took 
place  in  the  middle  of  the  Gault ;  since  the  fossils 


THE   STORY   OF  THE   EARTH. 


in  the  bottom  beds  of  the  red  limestone  include 
the  same  Gault  species  as  are  found  in  the  top 
beds  of  the  underlying  clay. 

A  similar  transition  in  physical  character  is 
seen  in  Norfolk  from  the  brown  sands,  locally 
termed  Carstone  at  Hunstanton,  to  the  sandy 
Hunstanton  limestone  which  there  rests  upon  it. 
This  succession  has  sometimes  led  to  the  belief 
that  the  upper  part  of  those  sands  is  of  the  age  of 
the  Lower  Gault. 

But  while  there  is  an  apparent  conformity  of 
the  Cretaceous  to  the  Neocomian  beds  on  the  east 
coast  of  England,  at  Speeton  there  was  a  manifest 
change  in  the  tilt  of  the  land  further  west,  which 
caused  the  sea  at  that  time  to  extend  over  the 

edges  of  the 
older  Secon- 
dary strata. 
This  is  seen  in 
land  in  the 
district  which 
is  now  East 
Yorkshire  by 
the  deposit  of 
the  Hunstan- 
ton limestone 
which  covers 
the  edges  of 
the  Oolitic 
rocks.  There 
appears  to  have  been  a  similar  depression  of  land 
at  the  same  time  to  the  west,  in  Dorsetshire  and 
Devonshire,  which  resulted  in  the  deposition  of 
sands,  known  as  the  Blackdown  Greensand,  over 
the  whole  of  the  Lower  Secondary  rocks,  and 
partly  upon  the  Carboniferous  rocks  about  Exeter, 


FIG.  28. — Ammonites  Deshayesii,  from  near 
the  base  of  the  Lower  Greensand,  Ather- 
field. 


LOWER  CRETACEOUS   STRATA.  151 

at  the  time  when  these  cretaceous  beds  began  to 
be  formed.  There  are  thus  sands  in  the  west  in 
Dorset  and  Devon,  which  appear  to  represent  a 
part,  if  not  the  whole,  of  the  Gault ;  perhaps  the 
Upper  Gault,  and  the  Upper  Greensand.  There 
is  a  Red  Limestone  in  the  north-east  from  Norfolk 
to  north  of  Flamborough,  which  is  a  similarly  un- 
divided deposit.  Placed  geographically  between 
these  sands  in  the  south-west  and  limestone  in  the 
north-east,  are  the  strata  known  as  Gault  and 
Upper  Greensand. 

The  Gault  rests  on  Lower  Greensand  and  Neo- 
comian  Sands.  It  is  a  blue  micaceous  clay,  dark 
in  colour  in  the  lower  part,  where  it  is  rich  in  fos- 
sils, and  full  of  layers  of  concretions  of  phosphate 
of  lime,  which  contains  a  large  amount  of  iron 
pyrites  in  some  localities.  Its  thickness  in  the 
south  of  England  is  about  150  feet,  but  it  thickens 
to  more  than  200  feet  at  Hitchin  ;  and  one  boring 
at  Soham  is  said  to  have  passed  through  450  feet 


E.  w. 

FIG.  29. — Cliff  section,  Hunstanton,  Norfolk.  Upon  the  brown 
Neocomian  Sandstone  is  the  red  Hunstanton  Limestone,  four 
feet  thick.  The  Lower  Chalk  rises  from  the  beach  to  the  top 
of  the  cliff,  the  dip  being  east. 

without  piercing  it.    Yet  it  thins  away  in  the  south 
of  Norfolk,  and  there  develops  calcareous  beds  in 


THE   STORY   OF   THE   EARTH. 


its  upper  part,  which  probably  show  that  the  Hun- 
stanton  limestone,  which  first  begins  to  be  recog- 
nised near  Sandringham,  includes  the  Upper  Gault. 
The  Gault  extends  as  a  clay  all  round  the  Weald, 
and  through  the  Isle  of  Wight ;  so  that  its  distri- 
bution is  connected  with  the  area  occupied  by  the 
Wealden  beds ;  and  the  changes  of  level  by  which 
that  district  was  effected. 

The  Upper  Greensand  generally  follows  the  dis- 
tribution of  the  Gault ;  but  there  are  certain  areas 
from  which  it  is  absent  as  a  recognisable  sand.  It 
is  well  developed  in  the  Isle  of  Wight,  and  extends 
from  Eastbourne  through  the  South  Downs  and 
through  the  greater  part  of  the  North  Downs;  but 
there  is  no  deposit  of  a  sandy  nature  in  the  Maid- 
stone  country,  found 
between  the  Gault  and 
the  chalk,  which  pass 
insensibly  into  each 
other.  From  Wiltshire 
the  Upper  Greensand 
extends  to  Tring,  as  a 
green  sand,  which  is 
there  about  30  feet 
thick;  east  of  Tring 
its  sandy  character  is 
lost.  It  has  been  found 
by  a  well  boring  again 
to  put  on  the  character 
of  a  green  sand  under 
Norwich.  All  the  intervening  country,  which 
Professor  Hull  regards  as  having  been  land,  dur- 
ing the  deposition  of  the  Carboniferous  limestone, 
is  covered  with  a  thin  bed  known  as  the  Cambridge 
Greensand,  which  is  not  more  than  a  foot  or  two  in 
thickness,  and  consists  of  nodules  of  phosphate  of 


FIG.  30. —Ammonites  planulatus, 
Cambridge  Greensand. 


LOWER  CRETACEOUS  STRATA.       153 

lime  embedded  in  a  paste  of  green  grains  of  glau- 
conite  and  marl,  which  entombs  the  most  remark- 
able assemblage  of  fossils  yielded  by  any  forma- 
tion in  Britain. 

When  this  bed  is  traced  north  it  is  lost ;  and  in 
so  far  as  can  be  judged  from  physical  evidence, 
and  its  fossils,  it  has  merged  in  the  Hunstanton 
limestone,  which  divides  into  three  thin  beds.  The 
middle  layer  of  that  rock  is  largely  formed  of 
concretions  of  phosphate  of  lime.  At  the  base  of 
the  chalk  wolds  the  limestone  augments  from  4 
feet  at  Hunstanton  to  a  considerable  thickness  at 
Speeton,  where  its  upper  beds  become  very  irreg- 
ular, and  pass  in 
to  the  white 
chalk  without 
stratigraphical 
planes  of  sepa- 
ration. The  ir- 
regular diffusion 
of  the  red  Col-  FIG.  31.— Part  of  the  stem  of  an  Encrinite 
rmr  in  nartQ  nf  (screw-stone),  derived  from  the  Car- 

boniferous  limestone    found    in    the 
the   Chalk  would  Cambridge  Greensand. 

appear    to    indi- 
cate that  the  colour  has  an  organic  origin. 

The  succession  of  the  Upper  Greensand  upon 
the  Gault  is  manifestly  a  consequence  of  upheaval 
of  the  old  land  from  which  the  Upper  Greensand 
was  derived,  bringing  the  source  of  the  sediment 
nearer ;  so  that  it  became  coarser.  The  Gault  at 
Ware  rests  directly  upon  the  Wenlock  limestone. 
At  Cheshunt  it  rests  upon  the  purple  Devonian 
mudstones.  Therefore  this  eastern  country  of 
England  gives  no  evidence  of  having  been  sub- 
merged during  all  the  Secondary  ages  till  the 
Gault  sea  spread  over  it,  and  Gault  was  laid  upon 


154        THE  STORY  OF  THE  EARTH. 

it.  And  since  some  fossils,  like  those  of  the  Car- 
boniferous limestone,  obviously  derived,  have  oc- 
curred in  the  Neocomian  beds  of  Upware,  and  in 
the  Cambridge  Greensand  (Fig.  31),  it  is  probable 
that  the  upheaval  which  brought  about  the  forma- 
tion of  the  Upper  Greensand,  raised  the  area  of 
ancient  rocks  beneath  the  Gault.  It  became  too 
shallow  for  the  accumulation  of  anything  but  the 
phosphatic  products  of  marine  animal  and  vege- 
table life,  boulders  of  the  parent  rocks,  slates, 
schists,  quartzites,  granites,  of  the  neighbouring 
land;  and  the  multitudinous  remains  of  Cimo- 
liosaurus  and  Ichthyosaurs,  and  Chelonians;  to- 
gether with  true  lizards,  allied  to  the  monitor; 
and  crocodiles  of  existing  types.  There  are  many 
terrestrial  saurians  allied  to  the  armoured  Scelt- 
dosaurus  of  the  Lias,  a  score  of  Pterodactyls  of 
all  sizes  of  the  genus  Ornithochirus.  One  Ptero- 
dactyle,  at  least,  is  toothless.  This  type,  which 
has  smooth  jaws  like  the  jaws  of  a  bird,  is  named 
Ornithostoma.  The  oldest  known  British  bird  is 
found  in  this  bed.  It  is  allied  to  the  divers. 

Cretaceous  Birds. 

The  oldest  British  fossil  bird  is  found  in  the 
Cambridge  Upper  Greensand.  The  bones  indi- 
cate an  animal  as  large  as  the  red-throated  Diver. 
Some  bones  are  like  the  living  genus  Colymbus; 
others  show  resemblances  to  Grebes  a'nd  Cormo- 
rants ;  and  possibly,  in  the  hip  girdle,  to  penguins. 
The  skull  is  singularly  like  that  of  the  red-throated 
Diver  in  size  and  form,  and  the  joints  of  the  back- 
bone are  similar,  but  not  identical.  The  femur,  the 
thigh-bone,  was  more  than  i£  inch  long;  and  the 
drumstick  bone  of  the  leg  develops  a  process  like 


LOWER  CRETACEOUS   STRATA.  155 

a  patella  at  the  knee-joint,  but  it  is  much  smaller 
than  in  the  Grebes.  The  bone  may  have  been  4 
inches  long.  The  metatarsus  differs  from  the 
bone  in  all  existing  birds,  because  it  shows  no 
sign  of  the  tarsal  bones  being  blended  with  it. 
It  was  probably  about  2^  inches  long,  so  that 
the  animal  may  not  have  exceeded  a  height  of  15 
inches.  It  is  unknown  whether  these  birds  pos- 
sessed wings.  The  saddle-shaped  mode  of  union 
between  the  vertebrae  of  the  neck  is  as  well  devel- 
oped as  in  existing  birds ;  but  it  is  either  absent 
in  the  back,  or  imperfectly  developed,  since  joints 
of  the  back-bone  have  the  ends  cup-shaped.  There 
is  no  evidence  that  the  tail  was  short.  It  is  cer- 
tain that  this  bird  was  a  water-bird,  and  it  prob- 
ably fed  under  the  water,  like  the  divers.  It  is 
named  Enaliornis.  In  the  Greensand  of  New 
Jersey  birds  have  also  been  found  which  show 
strong  affinities  with  the  living  divers;  and  since 
those  birds  possess  teeth,  it  is  not  improbable  that 
teeth  were  also  present  in  the  jaws  of  the  bird 
from  the  Cambridge  Greensand.  The  bi-concave 
condition  of  the  dorsal  vertebrae  of  Enaliornis  is 
also  found  in  one  of  the  American  genera. 

The  existence  of  these  fossils  goes  to  show 
that  the  family  of  divers  already  existed*  in  the 
cretaceous  seas;  and  that  their  jaws  were  armed 
with  teeth,  which  are  not  found  in  any  birds  of 
more  recent  date.  Birds  have  also  been  found 
in  the  Chalk  of  Seania  in  Sweden  but  the  bones 
are  few. 


156        THE  STORY  OF  THE  EARTH. 

CHAPTER  XIX. 

CHALK. 

THE  superposition  of  the  chalk  upon  the 
Upper  Greensand,  and  the  rocks  which  repre- 
sent it,  was  the  consequence  of  a  rapid  depres- 
sion of  old  continental  land  from  which  the  sedi- 
ments had  been  denuded  which  built  up  the  lower 
cretaceous  beds.  Land  did  not  entirely  disappear 
at  once.  There  are  a  few  places  in  Europe  in 
which  the  cretaceous  flora  is  met  with,  such  as 
Aix-la-Chapelle,  Halden  in  Westphalia,  Quedlin- 
burg  and  Blankenburg  in  the  Harz,  Molletin  in 
Moravia,  and  Niederschcena  in  Saxony.  The 
fossil  plant-life  found  in  these  localities  differs 
a  little,  but  includes  similar  types  to  those  in 
the  cretaceous  rocks  of  Greenland,  and  North 
America.  At  Aix,  the  cretaceous  basin  consists 
of  sands  and  sandstones  about  300  feet  thick, 
which  rest  upon  the  old  primary  rock  which  had 
been  a  land  surface.  The  sands  have  been  re- 
garded as  of  the  age  of  the  Upper  Chalk,  though 
they  contain  some  shells  of  the  age  of  the  Upper 
Greensand. 

The  chalk  abounds  in  scattered  fragments  of 
ancient  crystalline  rocks  in  its  lower  part.  In 
some  localities  in  the  south-east  of  England  its 
lower  beds  contain  enough  clay  to  give  it  an 
aluminous  odour;  while,  in  the  west  of  England, 
its  lower  beds  frequently  contain  grains  of  quartz. 
Proximity  to  land  is  indicated  almost  as  definitely 
by  the  preservation  of  branches  of  Sequoia,  in  the 
lower  chalk  of  Cambridgeshire,  and  all  through 
the  chalk  period  large  timber  trees  are  found 


CHALK.  157 

which  have  sunk  water-logged,  more  or  less  de- 
stroyed by  the  borings  of  the  ship  worm  Teredo. 
The  presence  of  the  remains  of  animals,  like  th^ 
flying  Ornithosaurs  and  the  long-bodied  lizard 
Dolichosaurus,  also  indicate  proximity  to  land. 
The  larger  part  of  the  chalk  is  supposed  to  have 
been  accumulated  in  moderate  depth  of  water, 
because  the  rock  almost  everywhere  shows  evi- 
dence of  slow  changes  of  currents  on  the  sea-bed. 
•  The  chalk  is  divided  into  four  deposits,  partly 
on  the  evidence  of  its  physical  characters,  and 
partly  from  the  nature  of  its  fossils.  The  lower 
part  of  the  rock,  often  termed  Chalk  Marl,  com- 
prises the  Grey  Chalk  of  Dover,  which  is  coloured 
with  clayey  matter,  and  is  known  as  the  Chalk 
Marl  and  Totternhoe  Stone.  The  bottom  beds 
contain  many  univalve  shells,  and  many  survivors 
of  the  remarkable  series  of  Cephalopods,  named 
Scaphites  (boat-shaped),  Turrilites  (spirally  tur- 
reted),  Baculites  (staff -like),  etc.,  which  are  so 
characteristic  of  the  Gault  and  Upper  Greensand. 

The  Lower  Chalk,  which  succeeds  the  Chalk 
Marl,  terminates  upward  in  the  bed  known  as 
the  zone  of  Holaster  sub-globosus.  It  is  thin  in 
the  eastern  counties,  but  becomes  thicker  in 
the  south  of  England.  It  is  covered  fay  the 
Melbourne  rock,  a  bed  formed  of  chalk  boulders, 
embedded  in  a  paste  of  chalk,  and  resting  upon 
a  plane  of  erosion  as  marked  as  that  by  which 
the  Cambridge  Greensand  rests. on  the  Gault, 
indicating  a  change  of  level,  which  uplifted  the 
underlying  deposit. 

The  overlying  beds  are  the  Middle  Chalk. 
This  part  of  the  chalk  lies  between  the  Mel- 
bourne Rock  below,  and  a  hard  phosphatic  bed 
above,  known  as  the  Chalk  Rock,  which  rings 


158        THE  STORY  OF  THE  EARTH. 

under  the  hammer.  Between  these  limits  the 
Middle  Chalk  is  about  350  feet  thick  in  Bucking- 
hamshire and  Bedfordshire,  and  more  than  200 
feet  thick  in  Cambridgeshire.  It  is  thinner  in 
the  North  Downs.  It  contains  some  thin  beds 
of  flint  in  the  Upper  part,  which  is  known  as  the 
zone  of  Holaster  planus.  The  Middle  Chalk  is  a 
great  lenticular  deposit,  which  is  frequently  marlyf 
as  though  a  quantity  of  clay  had  been  deposited, 
while  the  chalk  was  being  built  up,  by  the  growth 
of  its  characteristic  organisms.  This  portion  of 
the  chalk  has  been  thought  to  derive  its  clay 
from  the  old  land,  of  which  the  Cambridge  Green- 
sand  is  evidence  in  the  previous  period  of  time, 
the  intermixed  clay  being  the  finer  river  mud 
carried  out  into  the  ocean  from  a  region  of  an- 
cient and  crystalline  rocks  removed  to  a  greater 
distance  in  the  depression  of  land.  On  this  hori- 
zon there  are  multitudes  of  cup-sponges  with 
siliceous  skeletons,  of  the  genus  Ventriculites. 
The  Middle  Chalk  is  chiefly  conspicuous  for 
wanting  most  of  the  peculiar  Cephalopods  of  the 
Lower  Chalk,  and  for  wanting  the  sea-urchins  and 
starfishes  of  the  Upper  Chalk. 

The  Upper  Chalk,  which  is  only  about  250 
feet  thick  in  the  North  Downs  near  Croydon;  at- 
tains its  maximum  thickness  north  and  south.  At 
Norwich  it  is  about  500  feet  thick ;  and  in  the 
Isle  of  Wight  its  thickness  may  be  1000  feet.  At 
Lyme  Regis  its  thickness  appears  to  be  reduced 
to  50  feet.  It  is  whiter  and  softer  than  the  chalk 
below.  The  flint  which  characterises  it  occurs 
sometimes  in  horizontal  tabular  layers,  in  the 
planes  of  bedding.  Sometimes  they  are  in  con- 
cretionary nodules,  fantastically  irregular  in  form, 
which  are  not  absolutely  limited  to  the  planes  of 


CHALK. 


bedding;  occasionally  these  concretions  are  con- 
nected together  by  tabular  flint.  The  flint  nod- 
ules have  grown  since 
the  upheaval  of  the 
chalk,  and  they  are,  as 
a  rule,  scantily  devel- 
oped on  the  opposite 
side  of  a  slight  disloca- 
tion wherever  the  chalk 
has  been  strained  and 
fractured,  as  along  the 
valley  of  the  Thames. 
The  vertical  layers  of 
flint  which  have  been 
Henom'ted  in  surh  fk-  FlG*  32.— The  shepherd's  heart 
SUC£  r  sea-urchin,  Micraster  cor-an- 

SUrCS   have   CUt   Oil    the         guinum,  from  the  Upper  Chalk. 

water  supply;   so  that 

the  flints  are  large  on  one  side  of  such  a  barrier 

and  small  on  the  opposite  side. 

When  the  chalk  is  examined  under  the  micro- 
scope about  one-half  of  its  bulk  appears  to 
consist  of  microscopic  organisms,  of  the  group 
foraminifera,  some  of  which  appeared  in  the  old- 
est rocks  and  survive  at  the  present  day.  The 
more  important  of  these  foraminifera  comprise 
the  heavy  shell,  shaped  something  like  a  nautilus, 
named  Cristellaria,  the  broader  shell  more  like  an 
Ammonite,  named  Planorbulina,  the  spiral  shell 
resembling  a  pond  snail  Bulimina,  and  the  little 
Globigerina  formed  of  spheres,  which  succeed  each 
other  in  a  depressed  spire.  The  other  half  of  the 
chalk  consists  of  a  multitude  of  fragments,  large- 
ly formed  of  the  prisms  which  compose  shells  of 
mollusca,  flakes  of  the  shells  of  Terebratula  and 
Rhynchonella,  and  minute  fragments  of  corals  and 
Bryozoa;  and  when  these  organisms  cannot  be 


l6o        THE  STORY  OF  THE  EARTH. 

recognised,  the  material  is  amorphous  and  a 
product  of  decomposition  of  organisms.  This 
may  be  evidence  that  a  large  part  of  the  sub- 
^^^^  stance  of  the  chalk  not  only 

consists  of  the  remains  of 
animals  which  preserve  their 
forms,  but  that  the  remain- 
der of  it  passed  through  the 
bodies  of  animals  which  have 
left  little  other  record  of  their 
existence. 

_  The   fishes  are  the  chief 

FIG.  33.— The  base  of  Gal-   link  between  the  Chalk  and 
erites      sub-rotundus,   the  Upper  Greensand,  a  large 

sSngofthetheent±Pth   ™mber   of    small    sharks  of 
from  the  Upper  Chalk,   the  two  deposits  being  iden- 
tical.    There  is  the  greatest 

contrast  between  the  beds  in  mineral  character; 
and  in  the  principal  types  of  fossils,  because  the 
Upper  Greensand  gives  a  record  of  conditions  of 
the  shore  where  sediment  was  accumulating;  and 
the  chalk  gives  evidence  of  conditions  in  the  open 
sea,  almost  beyond  the  limit  to  which  sediment 
was  carried,  thus  demonstrating  how  great  the 
difference  in  fossils  may  be  with  a  slight  interval 
in  time.  The  conditions  compared  are  such,  in 
the  two  deposits,  as  may  be  found  on  the  one 
hand  on  the  south-west  shores  of  Ireland  at  the 
present  day,  and  on  the  other  hand  on  the  ocean 
floor  400  or  500  miles  to  the  west  in  the  Atlantic, 
where  an  organic  deposit  is  now  accumulating 
which  closely  resembles  the  chalk.  But  the  sharks 
on  the  Irish  coast  are  not  limited  to  the  shore, 
and  leave  their  remains  in  the  open  ocean  as  well ; 
exactly  as  happened  in  the  ages  of  the  Upper 
Greensand  and  chalk.  Just  as  sea-urchins  occur 


CHALK.  l6l 

scattered  through  the  chalk,  so  they  are  found 
living  on  the  chalky  floor  of  the  Atlantic  Ocean ; 
and  the  modern  representative  is  sometimes  very 
closely  allied  to  the  ancient  fossil. 

The  chalk  is  no  exception  to  the  law  that  the 
fossils  change  with  every  few  feet  of  a  deposit 
from  its  base  to  the  top.  Thus  there  are  nu- 
merous genera  of  sea-eggs  of  the  order  termed 
Echinoidea,  some  living  and  others  extinct  found 
in  the  Lower  Chalk  such  as  Salenia,  P seudodiadema 
and  Holaster.  Ananchytes,  Galerites,  Micr aster  and 
Cyphosoma  characterise  the  Upper  Chalk.  This 
succession  of  fossils  in  the  several  beds  of  chalk 
is  traced  through  the  country. 

There  is  no  evidence  in  the  chalk  itself,  at 
least  in  England,  of  its  deposition  coming  to  an 
end.  Its  newest  beds  at  Norwich  give  no  sign 
of  shallow  water  conditions.  Its  highest  beds  in 
Holland,  however,  are  the  yellow  granular  lime- 
stone of  Maestricht,  which  indicates  a  nearer  ap- 
proach to  a  shore  than  the  chalk  of  England.  In 
Denmark  univalve  shells,  which  from  time  to  time 
lived  in  the  chalk  sea  or  definite  horizons,  like 
the  Totternhoe  Stone  and  the  Chalk  Rock,  are 
found  in  the  newest  chalk  to  include  shells  which 
are  not  known  otherwise  till  the  tertiary  period, 
such  as  the  genera  Cyprcza  Oliva  and  Mitra.  They 
indicate  that  the  shore  conditions  of  the  chalk 
sea  are  returning  in  its  newest  beds  in  conse- 
quence of  a  general  upheaval  of  the  sea-bed  into 
land  in  the  European  region. 


ii 


1 62  THE   STORY   OF   THE   EARTH. 

CHAPTER   XX. 

LOWER    TERTIARY. 

THE  tertiary  rocks  occupy  the  basins  drained 
by  many  of  the  rivers  of  Europe.  And  although 
they  sometimes  occur  far  inland,  and  at  con- 
siderable elevations  above  the  sea,  as  in  the  Alps, 
Atlas,  and  many  of  the  mountain  chains  of  the 
old  world,  they  are  necessarily  among  the  most 
recently  elevated  parts  of  the  earth's  surface. 
Occasionally  there  is  a  possibility  that  one  de- 
posit extends  continuously  from  the  upper  creta- 
ceous to  the  lower;  Tertiary.  The  evidence  of 
this  continuity  in  time  is  only  found  in  North 
America,  in  the  "  Laramie  formation/'  in  which 
there  are  no  marine  fossils;  but  which  in  Texas, 
California  and  Brtish  North  America  abounds  in 
plant  remains,  and  yields  some  vertebrata  which 
favour  that  conclusion.  It  would  therefore  ap- 
pear that  in  some  parts  of  the  earth  there  is  no 
break  between  the  secondary  and  tertiary  rocks 
in  time,  any  more  than  between  the  other  rocks 
which  give  records  of  geological  time.  The  ter- 
tiary beds,  when  followed  in  their  succession  from 
the  oldest  to  the  most  recent,  show  an  increasing 
number  of  the  species  of  fossils  to  be  still  living, 
while  the  number  of  genera  which  are  extinct 
becomes  successively  smaller.  The  geographical 
distribution  of  the*  surviving  life,  however,  is  al- 
ways different  from  that  of  the  fossil  life.  There 
is  a  succession  of  tertiary  floras;  the  older  are 
Oriental  and  Malayan  and  Australian  in  their 
affinities;  succeeded  by  others  which  have  a 
greater  analogy  with  the  existing  flora  of  the 


LOWER  TERTIARY.  163 

western  part  of  North  America.  There  is  a  simi- 
lar geographical  relation  of  the  fossil  shells  in 
the  lower  Tertiary  rocks.  They  are  at  first  es- 
sentially the  shells  of  the  south  coast  of  Asia, 
but  afterwards  include  many  forms  which  can 
only  be  paralleled  at  the  present  day  at  our  Antip- 
odes, so  that  the  life  which  is  now  found  in  many 
distant  regions,  passed  in  successive  ages  over 
the  same  area  of  the  earth,  and  furnished  fossils 
to  the  rocks  which  were  laid  down  upon  succes- 
sive portions  of  the  sea-bed  as  it  slowly  moved 
onward. 

The  oldest  tertiary  strata  in  Europe  are  those 
of  Mons  in  Belgium,  where  the  chalk  is  bent  down 
into  a  trough,  which  received  the  waters  of  a  shal- 
low sea  at  an  earlier  period  than  the  chalk  of 
Great  Britain,  so  that  it  carries  an  older  deposit  of 
tertiary  age.  In  like  manner  the  east  of  England 
was  depressed  at  an  earlier  period  than  the  coun- 
try in  the  meridian  of  Reading,  so  that  the  beds 
in  the  eastern  part  of  the  Thames  basin  are  the 
oldest  in  the  British  tertiary  series.  The  Mon- 
ti,-m  fossil  shells  of  Belgium  include  many  which 
are  common  to  the  deposits  of  the  lower  tertiary 
period. 

Thanet  Sands. 

The  Thanet  Sands  are  the  oldest  tertiary  bed 
in  Great  Britain.  They  are  a  wedge-shaped  de- 
posit of  sand  which  occurs  in  the  east  of  the 
trough  known  as  the  London  basin.  It  is  90  feet 
thick  at  Canterbury  and  Herne  Bay,  and  thins 
westward,  being  absent  to  the  west  of  a  line  from 
Leatherhead  to  Hertford.  It  is  a  marine  de- 
posit, abounding  in  shells,  most  of  which  live  on 
into  the  London  clay.  There  is  a  Pholadomya,  a 


164        THE  STORY  OF  THE  EARTH. 

genus  which  survives  in  the  West  Indies,  and  the 
Nautilus  Sowerbii,  a  species  met  with  in  the  Lon- 
don clay,  but  most  of  the  other  fossils  are  of 
such  genera  as  occur  upon  the  British  shores  at 


E.  W. 

FIG.  34.— Cliff  section  of  the  Lower  Tertiary  Strata ;  east  of  Herne 

Bay  in  Kent. 

the  present  day.  The  commonest  are  species 
of  Cyprina  which  resemble  the  living  Cypriana 
Islandica.  The  sands  are  nowhere  consolidated ; 
usually  of  a  yellow  colour,  almost  free  from  any 
mixture  of  pebbles,  but  sometimes  yielding,  in 
the  east  of  Kent,  a  few  rounded  flints  which  show 
that  the  chalk  had  begun  to  be  denuded,  and  con- 
tributed some  particles  to  the  crystalline  grains 
of  quartz  which  form  the  sand.  Under  the  name 
Landenien  inferieur,  the  Thanet  Sands  are  traced 
into  Belgium,  being  well  seen  about  Brussels. 
They  are  also  traced  into  France  by  way  of 
Calais,  but  it  is  not  certain  that  they  extend  into 
the  Paris  basin.  The  land  surface  which  occurs 
at  Gelinden,  near  Liege,  makes  known  a  large 
flora  similar  in  some  respects  to  that  of  Aix,  with 
oaks  like  those  of  the  mountain  districts  of  Asia, 
with  laurels,  willow,  ivy,  and  other  familiar  types 
of  vegetation. 

Above  these  beds  succeed  the  Woolwich  and 
Reading  beds  25  feet  in  east  Kent  and  90  feet 
under  London.  They  are  the  upper  Landenien 
of  Belgium  and  the  north  of  France,  sometimes 


LOWER    TERTIARY.  165 

known  as  the  zone  of  Ostrea  bellovacina^  and 
Pectunculus  terebratularis.  Ascending  the  Thames 
these  beds  are  at  first  marine  sands,  differing  but 
little  from  the  Thanet  Sands.  At  Upnor,  near 
Rochester,  they  become  estuarine,  and  consist 
of  layers  of  rounded  pebbles  and  alternations  of 
clay,  sands  and  shell  beds.  This  condition  con- 
tinues up  the  Thames  valley,  and  the  marine 
shells,  which  were  scarcely  distinguishable  from 
the  shells  of  the  Thanet  Sands  at  Herne  Bay, 
give  place  to  fresh-water  shells  under  London. 
At  Loampit  Hill  re- 
mains of  terrestrial 
plants  and  insects  also 
occur.  At  Reading 
there  is  a  flora  of 
matted  leaves,  referred 
to  species  of  fig  and 
laurel  and  allies  of  the 
evergreen  oak,  in  the 
lower  part  of  the  sands. 
These  deposits,  which 
were  formed  in  fresh 
water,  alternate  with 
beds  containing  ma- 
rine shells  which  have 

a  Inn  a-  rsna-^  in  timf>  FlG-  35-— Ostrea  belloVkcina,  from 
a  long  range  m^time,  the  Thanet  Sands.  Theshellhas 
Some  Occurring  in  the  grown  on  a  branch  of  a  tree. 

Montian  beds  and  sur- 
viving to  the  London  clay.  It  is  therefore  shown 
by  these  Woolwich  and  Reading  beds  and  their 
fossils  that  the  dome  of  the  Wealden  district,  be- 
tween the  Thames  and  the  English  Channel,  was 
raised  into  land;  and  that  the  chalk  which  once 
covered  it  furnished  the  flints  which  were  rolled 
into  completely  rounded  pebbles  before  they  were 


1 66  THE  STORY  OF  THE  EARTH. 

swept  down  into  these  tertiary  beds,  which  are 
now  exposed  on  the  northern  slope  of  the  North 
Downs. 

With  the  oscillations  in  level  a  part  of  this 
land  area  at  least  supported  the  vegetation  which 
furnished  those  beds  of  lignite  which  extend  by 
Woolwich  and  Bromley,  and  the  forest  trees,  which 
show  by  their  leaves  a  marked  resemblance  to 
those  of  Gelinden.  This  indicates  that  the  an- 
cient connection,  by  continuous  land,  between 
the  south-east  of  what  is  now  England  and  Bel- 
gium and  Hanover,  was  maintained  in  the  tertiary 
period  just  as  it  had  been  in  the  older  epoch  of 
the  Weald. 

In  one  locality,  near  Rheims  in  France,  the 
lower  tertiary  beds  have  yielded  many  remains 
of  mammals  which  fore- 
shadow lemurs  and  ro- 
dents. Among  these  oc- 
curs the  Neoplagiaulax 
which  seems  like  a  sur- 
vival of  the  Plagiaulax  of 
the  Purbeck  beds.  This 
is  worth  recalling  on  ac- 
count  of  the  resemblance 

FIG.    36.-Cyprina   Morrisi  in     °f.  ^    tertiary   plants   of 

Thanet  Sand.  this  horizon  with  the  cre- 

taceous  flora.  The  Lon- 
don clay  indicates  depression  which  banished  the 
shores  of  the  tertiary  land  to  some  distance. 
There  are  oscillations  in  its  level  which  varied 
both  the  mineral  character  of  the  stratum  and 
the  fossil  life. 

At  the  base  there  is  usually  a  bed  of  small 
rounded  flint  pebbles  known  as  the  basement 
bed,  with  sharks'  teeth.  The  clay  gives  evi- 


LOWER   TERTIARY.  167 

dence  at  its  base  of  terrestrial  life,  and  near 
proximity  to  land,  in  the  presence  of  a  few 
mammals,  some  of  which  are  allied  to  the  exist- 
ing tapirs.  With  these  are  found  crocodiles  of 
the  type  now  living,  and  fresh-water  tortoises, 
such  as  frequent  estuaries  at  the  present  day. 

The  middle  of  the  clay  abounds  in  crabs  and 
lobsters.  While  the  top  bed,  about  50  feet  thick, 
is  rich  in  plants  represented  by  the  fruits  of  a 
large  flora.  The  upper  beds,  like  the  basement 
beds,  are  sandy.  At  Bognor  the  sand  at  the  base 
is  calcareous  and  concretionary,  with  many  marine 
fossil  shells. 

The  London  clay  is  500  feet  thick  in  Essex  and 
Sheppey.  It  thins  to  the  west  and  south-west ;  be- 
ing 400  feet  under  London,  300  at  Southampton, 
200  at  Alum  Bay  and  100  at  Studland  Bay  on  the 
opposite  coast.  To  the  south-east  it  is  thickened 
with  the  sands  in  its  lower  part.  Its  fossil  shells, 
such  as  Cyprea,  Murex,  Conus,  Pleurotoma,  Fusus, 
are  of  types  which  abound  in  the  seas  to  the  south 
of  Asia.  The  plants  which  occur  in  its  uppermost 
part  also  have  an  Asiatic  character.  The  conifers 
are  well  represented  by  Cypresses,  the  Sequoia, 
Pines,  and  the  Yew  Salisburia.  The  lilies  include 
the  so-called  American  aloe,  Agave.  A  species  of 
Smilaoc  represents  the  Sarsaparilla  tribe.  Bananas 
are  known  from  the  genus  Musa.  The  ginger 
order  is  represented  by  Amomum  which  yields 
Cardamoms.  Nipa,  a  screw  pine  common  on  the 
banks  of  the  Ganges  and  in  the  Malay  peninsula, 
is  by  far  the  most  abundant  fruit.  It  is  associated 
with  many  palms,  among  which  the  areca  palm,  the 
nutmeg  type,  the  fan  palm  of  the  south  of  Europe 
Chamerops,  and  the  great  palm  Sabal  are  conspicu- 
ous. The  oak,  hazel,  walnut,  liquid  amber,  laurel, 


1 68  THE  STORY  OF  THE  EARTH. 

magnolia,  ebony  and  spurge  are  present,  as  are 
representatives  of  some  medicinal  plants  like 
StrychnoS)  which  yields  nux  vomica,  and  of  Cin- 
chona, which  yields  quinine.  There  are  represent- 
atives of  the  tomato  and  melon.  Apples  are 
represented  by  Cotoneaster,  and  associated  with 
almonds  and  plums.  The  cocoa  is  represented 
by  a  species  of  Theobroma.  There  are  several 
limes  and  maples.  Water-lilies  are  represented 
by  the  Lotus,  and  the  Victoria  lily  of  tropical 
America. 

The  London  clay  is  well  developed  in  Belgium 
and  in  the  north  of  France.  It  does  not  reach  the 
Paris  basin  in  a  recognisable  form  ;  though  it  may 
be  represented  by  the  lignites  and  sands  of  the 
Soissonnais.  But  neither  the  lignites  in  France, 
nor  the  Ypresien  beds  which  represent  the  London 
clay  in  Belgium,  yield  the  abundance  of  fruits 
which  is-  met  with  in  the  Isle  of  Sheppey.  Some 
of  the  Belgian  specimens  of  Nipa  are  much  better 
preserved  than  the  macerated  and  compressed 
fruits  of  Sheppey,  as  though  they  were  deposited 
without  being  so  long  in  the  water. 

Above  the  London  clay  are  the  sands  which 
cap  the  hills  at  Harrow,  Hampstead,  Highgate, 
High  Beech,  Haveringate  and  many  places  in 
Essex,  having  formerly  been  spread  continuously 
all  over  the  London  clay,  as  they  still  are  between 
Egham  and  Aldershot.  They  form  Ascot  Heath 
and  Bagshot  Heath,  and  are  known  as  the  Bagshot 
Sands. 

The  lower  part,  termed  Lower  Bagshot  Sands, 
thickens  in  the  Isle  of  Wight  to  about  800  feet, 
and  forms  the  brilliantly  coloured  vertical  sands 
of  Alum  Bay.  They  are  laminated  with  films  of 
clay  at  Woking,  where  the  thickness  is  about 


LOWER  TERTIARY. 


169 


ioo  feet.  Beds  of  pipeclay  frequently  occur; 
and  occasionally,  as  at  Newbury,  the  pipeclay 
contains  fossil  leaves  like  those  at  Bournemouth. 
In  the  Isle  of  Wight  the  bands  of  pipeclay  are 
exceptionally  pure,  as  though  they  had  been  de- 
rived from  white  felspar,  but  never  extend  far. 
They  are  usually  only  a  few  inches  thick,  though 
occasionally  thick  beds  are  found.  From  them  a 
flora  has  been  obtained,  which,  although  known 
only  from  the  leaves  of  plants,  indicates  many  of 
the  types  at  the  top  of  the  London  clay  which  are 


HCADON  HILL 


N.  S. 

PIG.  37. — Cliff- section,  Alum  Bay,  Isle  of  Wight,  showing  the  rela- 
tion between  the  vertical  eocene  beds  of  Alum  Bay  and  the 
more  horizontal  oligocene  strata  of  Headon  Hill.  , 

known  only  from  fruits;  so  that  they  may  well  be 
regarded  as  a  surviving  part  of  the  vegetation  of 
the  London  clay.  Among  these  Alum  Bay  plants 
are  some  of  the  Cypresses  and  Sequoia,  Smilax  and 
the  palm  Sabal  is  identified  in  both.  There  is  the 
same  arum  named  Aronium.  The  oak,  walnut, 
laurel,  cinchona,  ebony,  magnolia,  maple,  the 
soapworts  Sapindlus  and  Cupania,  the  allspice 
and  Eucalyptus,  the  almond  and  plum,  and  the 


170       THE  STORY  OF  THE  EARTH. 

mimosas  are  common  to  both  deposits.  Besides 
these,  the  Alum  Bay  beds  make  known  many  new 
types,  of  which  the  London  clay  gives  no  evi- 
dence. Among  them  are  the  beech,  elm,  fig,  bread 
fruit,  willow,  poplar,  sandalwood,  the  Mezereon, 
Aristolochia,  olive,  ash,  convolvulus,  verbena,  bil- 
berry, some  heaths,  the  aralia,  dogwood,  white 
water-lily,  custard  apple,  holly,  buckthorn,  vine, 
sumach  and  pistachio.  These  are  among  the  more 
important  new  plants  introduced  in  the  Bagshot 
Sands  ;  and  with  them  are  a  number  of  Proteacese, 
referred  to  genera  now  living  in  Australia,  as  well 
as  a  representative  of  the  type  genus  Proteoides, 
the  sugar  bush  of  South  Africa.  One  of  the  most 
striking  features  in  the  flora  is  the  small  number 
of  palms,  and  the  absence  of  the  Nipa,  which  in 
Sheppey  is  the  predominant  fruit  and  is  present 
in  the  newer  beds  at  Bournemouth.  The  fruits 
and  leaves,  like  the  shells  in  the  associated  strata, 
indicate  affinities  with  the  life  of  far-off  regions  of 
the  earth.  It  is  a  generation  since  Unger,  a  Vien- 
nese student  of  the  fossil  plant-life  of  the  lower 
tertiaries,  impressed  with  the  occurrence  of  nu- 
merous genera  in  Austria,  which  live  at  the  pres- 
ent day  in  Australia,  regarded  the  eocene  flora  as 
indicating  a  migratory  passage  of  the  ancient 
plants  from  Europe  into  the  Australian  region. 
The  plane  of  junction  where  the  Bagshot  Sands 
come  to  an  end,  and  the  succeeding  marine 
Bracklesham  beds  begin  is  not  easy  to  draw ;  be- 
cause the  Bracklesham  beds  contain  locally  thick 
layers  of  lignite,  which  have  the  aspect  of  a  coal 
seam,  and  indicate  the  persistence  of  terrestrial 
conditions  and  some  oscillations  of  that  terres- 
trial surface  in  level. 

Low  down   in  these  beds  is  found  the  large 


LOWER   TERTIARY.  171 

foraminiferous  shell  named  Nummulites  Zczvigatus. 
It  does  not  form  a  thick  bed ;  but  probably  marks 
the  geological  horizon  of  the  Nummulitic  Lime- 
stone, which  is  one  of  the  most  important  lime- 
stones in  the  old  world,  and  extends  from  the 
Alps  and  Carpathians  into  Thibet,  and  from  Mo- 
rocco, Algeria  and  Egypt  through  Cabul  and  the 
Himalayas  to  China. 

In  Great  Britain  the  Bracklesham  beds  in  Sus- 
sex and  the  Isle  of  Wight  are  alternations  of 
green  sands  and  sandy  clays,  which  are  separated 
from  the  overlying  Barton  clay  by  a  conglomerate 
formed  of  rounded  flint  pebbles.  At  Bournemouth 
their  character  has  changed.  They  are  foxy-brown 
estuarine  sands  with  beds  of  pipeclay,  in  which 
occurs  another  flora,  with  many  ferns,  palms,  cac- 
tus, eucalyptus,  figs,  willows,  beech,  and  nipa. 
The  cactus  is  an  American  type.  Subsequently 
the  North  American  type  of  vegetation  became 
more  abundant  in  Europe  in  the  middle  Tertiary 
period,  and  better  defined  by  many  genera.  The 
Barton  clay  succeeds  the  Bracklesham  beds.  It  is 
a  blue  clay,  about  300  feet  thick,  with  an  extraor- 
dinary number  of  fossil  shells,  many  of  which  are 
similar  in  genera  to  those  found  in  the  London 
clay  and  Bracklesham  beds,  though  tj^e  clay  is 
characterised  by  the  abundance  of  individuals  of 
the  genera  Chama,  Crassatella,  Fusus,  and  Valuta , 
and  by  the  presence  of  some  peculiar  genera  like 
Typhis,  a  univalve  similar  to  Murex,  except  that 
the  spines  are  tubular.  There  is  no  such  fauna 
anywhere  to  be  met  with  at  the  present  day.  It 
is  not  unlike  a  blending  of  the  existing  Malayan 
and  New  Zealand  forms  of  marine  life ;  and 
many  of  the  shells,  like  the  Crassatella,  Typhis, 
Chama,  Pecten,  Pectunculus,  are  very  similar  to 


172       THE  STORY  OF  THE  EARTH. 

species  now  living  in  or  about  the  New  Zealand 
seas. 

The  Bracklesham  beds  have  generally  been  re- 
garded as  represented  by  the  Calcaire  grossier  of 
the  Paris  basin,  while  the  Barton  clay  corresponds 
to  the  grits  with  the  Nummulites  variolarius,  and 
some  newer  deposits,  such  as  the  Ores  de  Beau- 
champ.  These  beds  are  well  represented  in  Bel- 
gium. The  Bracklesham  beds  have  yielded  some 
interesting  serpents  of  the  genus  Palaophis  though 
not  so  large  as  those  of  the  London  clay.  In  the 
Barton  clay  occurs  a  marine  mammal,  of  the  genus 
Zeuglodon  shown  by  its  back  bone  to  be  a  true 
whale,  which  has  the  teeth  double-rooted  and  ser- 
rated in  a  way  that  is  seen  in  no  other  animal, 
though  resembling  some  seals. 

The  Barton  period  comes  to  an  end  with  a 
deposition  of  200  feet  of  sand,  in  which  fossils 
are  rare. 

Theoretically,  the  Bracklesham  and  Barton 
beds  together  are  an  immense  expansion  of  the 
middle  50  feet  of  the  Bagshot  sands  at  Aldershot, 
which  contain,  in  some  of  the  clayey  layers,  im- 
pressions of  fossils  which  appear  to  be  identical 
with  those  found  at  Barton  in  Hampshire,  and 
Bracklesham  in  Sussex.  On  this  hypothesis  the 
Bracklesham  and  Barton  beds  indicate  in  the 
Hampshire  area  a  depression  of  the  old  sea-bed, 
into  which  peculiar  faunas  successively  moved. 
The  upper  Bagshot  or  Barton  sands  bring  back 
again  the  conditions  of  a  shoal,  or  shore,  due 
to  a  general  uprising  of  the  land.  The  few 
shells  which  have  been  found  in  them  are  Barton 
species. 

The  sea-bed  continued  to  be  elevated  until 
it  passed  into  a  land  surface,  in  the  succeeding 


MIDDLE  TERTIARY.  173 

period  of  time  termed  Oligocene,  which  is  the  only 
part  of  the  middle  Tertiary  represented  in  Great 
Britain. 


CHAPTER   XXI. 

MIDDLE     TERTIARY. 

THE  Middle  Tertiary  period,  usually  termed 
Miocene,  makes  a  more  striking  approximation  in 
its  life  to  the  animals  and  plants  which  exist  at 
the  present  day.  In  the  European  area  it  is  a 
"record  of  terrestrial  and  lacustrine  conditions, 
alternating  with  the  deposits  or  shallow  seas. 

In  Great  Britain  only  a  portion  of  the  earlier 
part  of  the  Miocene  period  is  represented  by  de- 
posits which  now  cover  the  northern  part  of  the 
Isle  of  Wight,  much  of  the  New  Forest,  and  are 
exposed  in  the  cliffs  at  Hordwell,  Tollands  Bay, 
at  Bembridge  and  Hempstead.  These  strata  are 
grouped  together  as  Oligocene. 

Headon  Beds. 

The  oldest  oligocene  beds,  knowp  as  the 
Headon  series,  are  130  feet  thick  at  Headon  Hill, 
in  the  Isle  of  Wight,  are  in  the  main  fresh-water 
strata.  They  comprise  first,  about  70  feet  of 
brackish  water  marls,  and  fresh-water  limestones, 
superimposed  upon  the  marine  sands  above  the 
Barton  series.  This  proves  that  the  shallow  sea, 
with  the  Upper  Bagshot  Sands  for  its  floor,  had 
become  converted  into  dry  land,  upon  which 
lakes  were  formed  by  fresh  waters  draining  into 
the  bottom  of  the  trough  from  a  limestone  region 
such  as  the  chalk  or  the  oolites. 


174        THE  STORY  OF  THE  EARTH. 

The  strata  and  their  fossils  show  that  the 
level  of  the  land  fluctuated.  The  lakes  became 
sometimes  occupied  with  brackish  water,  so  that 
marine  life  divides  up  the  fresh-water  deposits. 
After  the  lower  fresh-water  beds  were  formed, 
the  land  was  submerged,  so  as  to  give  rise  to  the 
Middle  Headon  beds,  which  are  essentially  ma- 
rine. There  are  great  banks  of  oysters  with  nu- 
merous marine  shells,  most  of  them  similar  to  the 
types  which  had  previously  been  known  in"  the 
Barton  clay.  These  marine  beds  became  tje?ter 
developed  at  Brockenhurst  in  the  New  Forest, 
where  some  corals  are  found,  together  with  the 
vertebral  column  of  Zeuglodon,  a  marine  mammal 
of  the  whale  type,  with  teeth  like  seals,  already 
known  from  the  Barton  clay.  These  marine  beds 
are  widely  spread  in  Germany.  After  they  were 
deposited  the  land  was  raised  once  more,  and  the 
Upper  Headon  beds  formed,  which  reach  a  con- 
siderable thickness.  They  are  fresh-water  de- 
posits, consisting  of  marls  frequently  green,  full 
of  the  large  Paludina  lenta,  the  Cyrena  obovata  and 
the  extinct  Potomomya  plana^  which  alternate  with 
thick  limestones,  commonly  full  of  fresh-water 
shells  of  the  genera  Planorbis  and  Limncea.  These 
limestones  are  almost  entirely  the  product  of  the 
growth  and  decay  of  the  fresh-water  plant  Chara 
which  precipitates  carbonate  of  lime  upon  its 
tissues  by  absorbing  carbonic  acid  gas  from  the 
water  charged  with  carbonate  of  lime.  In  these 
limestones  remains  are  found  of  terrestrial  mam- 
mals of  the  types  present  in  the  Gypseous  beds 
at  Paris,  although  they  are  not  so  numerous  as  in 
the  Bembridge  beds. 

When  the  Headon  beds  are  followed  to  the 
coast  of  Hampshire,  the  limestones  disappear, 


MIDDLE   TERTIARY.  175 

leading  to  the  conclusion  that  the  upheaval  of 
the  chalk,  which  now  runs  in  a  nearly  vertical 
position  through  the  Isle  of  Wight,  had  already 
begun  to  supply  the  calcareous  matter,  which  the 
streams  brought  into  the  lakes  of  the  Headon 
period. 

The  beds  which  rest  upon  the  Upper  Headon 
strata  are  termed  the  Osborne  or  St.  Helen  s  series. 
They  are  sandstones  and  marls,  much  thicker 
than  any  of.  the  sandstones  and  marls  in  the 
Headon  beds,  and  therefore  in  contrast  to  them. 
Some  of  the  sandstones  become  calcareous,  and 
pass  into  concretion- 
ary limestones.  The 
shells  are  all  of  fresh- 
water types.  The 
sandstones  are  some- 
times ripple -marked, 
probably  by  the  wind. 

The  Osborne  beds 
are  about  80  feet 
thick,  and  divide  the 
Headon  from  the  Bern- 
bridge  beds.  The 

RoTHhn'Ja-p   Ti*nfistni>tp\*  FIG.  38.— Planorbis  euomphalus  and 

other  fossils  in   the   fresh-water 
thick,     very     like     the        Headon  limestone.' 

Headon       limestones, 

rather  creamy  in  colour,  full  of  the  same  types 
of  fresh-water  shells,  and  containing  many  land 
shells,  especially  examples  of  the  genera  Helix, 
Bulimus,  and  Glandina.  These  land-shells  have  a 
marked  affinity  with  species  now  living  in  North 
America,  with  which  one  or  two  may  be  identical. 
The  Bembridge  limestone  abounds  in  seed-vessels 
of  the  plant  Chara,  which  formed  it.  Remains 
occur  in  it  of  several  species  of  the  extinct  mam- 


1 76  THE  STORY  OF   THE  EARTH. 

mal  P alaotherium  which  in  some  ways  approxi- 
mated in  structure  to  existing  tapirs. 

Where  this  limestone  caps  Headon  Hill  it  is 
about  15  feet  thick.  The  Bembridge  marls  rest 
upon  it  successively  in  the  section  at  Hempstead. 
They  are  grouped  into  a  number  of  sandy  beds 
and  shaly  clays,  full  of  estuarine  shells,  among 
which  are  the  genera  Melania  and  Melanopsis, 
which  alternate  with  beds  containing  Cyrena  and 
other  bands  in  which  the  shells  are  of  fresh  water 
species. 

The  top  of  the  marls  is  the  remarkable  thin 
deposit  known  as  the  Black  Band  which  is  usually 
grouped  with  the  overlying  Hempstead  series. 

The  Hempstead  Beds. 

Hempstead  Hill  lies  to  the  east  of  Yarmouth 
in  the  Isle  of  Wight,  on  the  shore  of  the  Solent. 
It  is  formed  of  about  170  feet  of  fresh-water  and 
estuarine  marls,  capped  by  a  marine  stratum. 
The  marls  have  a  general  resemblance  to  the 
Bembridge  marls.  The  Black  Band  at  the  base 
is  about  two  feet  of  clay,  coloured  with  vegetable 
remains,  among  which  Sequoia  and  water-lilies 
have  been  recognised,  together  with  the  teeth  of 
P alaotherium  and  other  mammals  and  remains  of 
tortoises  and  crocodiles.  It  is  an  old  terrestrial 
surface  on  which  rest,  first,  the  lower  marls  with 
Melania  muricata ;  secondly,  the  middle  marls 
with  Cerithium  Sedgwicki;  and  thirdly,  the  upper 
marls  with  Cerithium  plicatum.  At  the  top  are  the 
Corbula  beds  which  contain  several  marine  shells 
in  addition  to  the  estuarine  forms,  among  them 
Valuta  Rathiera,  Natica,  Corbula,  and  a  species 
of  oyster.  The  characteristic  mammal  of  these 


MIDDLE  TERTIARY.  177 

beds  is  the  Hyopotamus.  These  are  the  newest 
British  deposits  in  the  Isle  of  Wight  of  oligocene 
age. 

The  lignites  alternating  with  clays  which  fill 
up  the  basin  at  Bovey  Tr^cey  in  Devonshire  are 
probably  of  the  same  age.  They  form  deposits 
about  300  feet  thick ;  probably  once  thicker. 
With  the  exception  of  a  single  beetle,  the  remains 
found  in  them  are  about  fifty  species  of  plants. 
The  lignite  itself  is  chiefly  the  flattened  trunks  of 
the  Sequoia  Couttsia.  About  half  the  plants  are 
regarded  as  of  peculiar  species  and  the  remain- 
ing twenty-five  occur  in  the  Miocene  of  Germany 
and  Switzerland.  Among  these  trees  are  species 
of  fig,  oak,  laurel,  cinnamon,  the  sour  gum  tree 
Nyssa,  a  palm,  vine,  and  some  ferns  such  as 
Lastrea. 

On  the  Continent  the  Miocene  beds  attain 
singular  importance.  Not  only  from  the  part 
they  take  in  forming  the  basins  drained  by  so 
many  rivers,  and  in  the  structure  of  the  Alps,  but 
also  on  account  of  the  remarkable  mammalian 
remains  which  they  yield. 

The  Dinotherium,  which  appears  to  have  been 
a  sort  of  Mastodon  with  tusks  in  its  lower  jaw, 
is  one  of  these.  The  three-toed  horse*  named 
Hipparion,  is  even  more  interesting,  while  the 
fossils  obtained  at  Pikermi,  near  Athens,  include 
giraffes  and  many  other  animals  which  have  long 
passed  away  from  Europe.  Perhaps  the  most 
extraordinary  Miocene  fauna  is  found  fossil  in 
the  Siwalik  Hills  in  India,  which  lie  between  the 
Jumna  and  the  Ganges,  and  rise  to  a  height  of 
2000  or  3000  feet.  The  species  of  Hippopotamus, 
and  allies  of  the  giraffe  and  other  African  types 
which  are  there  found,  testify  that  change  of 

12 


178        THE  STORY  OF  THE  EARTH. 

area  in  the  distribution  of  genera  on  land  in  the 
Tertiary  period,  continued  as  persistently  as  the 
migrations  of  marine  life  in  the  Primary  period. 


CHAPTER  XXII. 

THE    CRAG. 

AFTER  the  great  terrestrial  epoch  of  the  newer 
Miocene  period  had  passed  away  entirely  unrepre- 
sented by  strata,  in  Great  Britain,  deposits,  named 
the  Crag,  are  found,  which  fringe  the  coast  in 
Norfolk,  Suffolk,  and  Essex,  occur  in  a  few  places 
in  Kent ;  and  in  Belgium. 

The  relative  age  of  these  beds  was  first  deter- 
mined by  the  method  of  counting  the  number  of 
existing  species  in  each  of  the  tertiary  strata.  On 
that  basis  the  tertiary  epoch  had  been  divided  into 
Eocene,  or  lower  Tertiary,  Miocene,  or  middle 
Tertiary,  and  Pliocene,  or  upper  Tertiary.  Sub- 
sequently the  Lower  Miocene  was  named  Oligo- 
cene.  In  the  Pliocene  the  fossils  include  more 
than  35  per  cent,  of  living  species. 

In  this  great  period  the  Crag  finds  a  place 
The  older  beds,  named  Coralline  Crag,  have  84 
per  cent,  of  the  shells  still  living;  and  in  the 
newer  or  Red  Crag  92  per  cent,  of  the  shells  still 
exist. 

The  Coralline  Crag  rests  unconformably  upon 
the  London  clay.  Its  lower  part  consists  of  yel- 
low false  bedded  sands,  which  sometimes  form  a 
building  stone  about  30  feet  thick.  This  sand 
appears  to  have  been  derived  from  denudation  of 
the  Bagshot  sands  which  once  extended  over  the 


THE   CRAG.  179 

whole  area  of  the  London  clay.  The  shelly  beds 
include  a  number  of  kinds  of  life  which  are  now 
only  represented  in  southern  seas.  As  many  as 
two  hundred  species  are  said  to  be  found  living 
in  the  Mediterranean,  and  a  few  are  paralleled  off 
the  coasts  of  "Japan,  Mexico  and  the  West  Indies. 
But  while  about  sixty-five  of  the  species  are 
known  only  in  southern  seas,  fourteen  only  in* 
northern  seas,  and  seventeen  have  been  met  with 
in  no  other  deposit,  there  are  as  many  as  185 
Coralline  Crag  shells  still  found  in  the  British 
seas. 

.The  rock  is  named  Coralline  Crag  from  the 
large  extent  to  which  its  upper  beds  consist  of 
the  remains  of  Polyzoa  which  were  formerly 
termed  corallines.  Of  those  Polyzoa  which  are 
still  living,  26  out  of  30  are  met  with  in  British 
seas,  but  the  majority  of  the  fossils  belong  to  the 
two  extinct  types  Alveolaria  semiovata,  and  Fasicu- 
laria  aurantium  with  which  are  some  species  of 
the  genera  Retepora  Idmonea  and  Eschara.  The 
fishes  of  this  crag  include 
the  common  cod,  green 
cod,  power  cod,  the  pol- 
lack, whiting,  and  whiting 
pout,  with  which  have  been 
found  the  great  teeth  of 
the  shark  Carcharodon,  and 
of  Otodus. 

At  the  base  of  the  Cor- 
alline Crag,  in  places  where 
the  shark's  teeth  are  found  FlG  39._Cardita  senilis>  from 

IS    a    bed     of     nodules     Of  the  Coralline  Crag. 

phosphate  of  lime,  in  which 

bones  of  the  dolphin  Choneziphius  occur  with  teeth 

of  the  whale  Balcenodon,  associated  with  teeth  of 


180       THE  STORY  OF  THE  EARTH. 

deer,  rhinoceros  and  Mastodon  which  were  obvi- 
ously derived  from  a  land  surface,  and  perhaps 
from  an  older  deposit.  In  this  bed  are  multitudes 
of  fossils  from  the  London  clay,  and  a  few  croco- 
diles and  Plesiosaurs  derived  from  the  older  Sec- 
ondary rocks. 

The  characteristic  shells  of  the  Coralline  Crag, 
besides  the  comparatively  rare  species  of  Voluta, 
Cassidariay  Pyrula  and  Lingula,  include  many  spe- 
cies of  the  genus  Astarte.  That  genus  which  now 
characterises  northern  regions,  is  here  repre- 
sented by  multitudes  of  individuals.  The  Cypri- 
ana  islandica,  Terebratula  grandis,  Cardita  senilis, 
Buccinum  dalei  are  typical  fossils. 

The  Red  Crag. 

After  the  Coralline  Crag  was  formed  in  some 
tranquil  depth  of  water,  the  shores  appear  to  have 
been  upheaved.  And  on  the  eroded  surface  about 
20  feet  of  false  bedded  sands  and  comminuted 
shells  were  laid  down,  as  shore  deposits,  which 
fringe  the  island-like  masses  of  white  or  coralline 
crag.  This  newer  deposit,  named  Red  Crag,  indi- 
cates three  or  four  successive  depositions.  Each 
of  its  beds  was  planed  level  by  denudations,  which 
left  thin  layers  of  pebbles  and  nodules  of  phos- 
phate of  lime  at  the  junctions. 

It  has  been  observed  that  the  older  Red  Crag 
at  Walton  on  the  Naze,  has  fossils  more  like  the 
species  of  the  Coralline  Crag  than  are  found  else- 
where. At  Butley  a  zone  abounds  in  northern 
species,  and  on  this  is  a  newer  crag  still.  The 
Red  Crag  along  the  river  Deben  contains  a  larger 
number  of  terrestrial  mammals  than  has  been 
found  at  the  base  of  the  Coralline  Crag.  The 


THE   CRAG.  l8l 

additional  types  comprise  species  of  tapir,  the 
Siwalik  Hycenarctos,  hyaena,  Hipparion^  besides 
deer,  bear,  and  among  marine  animals  a  Halithe- 


FIG.  40. — Fusus  antiquus  reversed  variety,  from  the  Red  Crag. 

rium  and  a  walrus  with  large  tusks.  The  shells 
are  interesting  from  the  dominance  of  a  few 
types,  such  as  the  reversed  variety  of  the  Fusus 
antiquus,  which  is  associated  with  the  common 
whelk,  the  European  cowrie,  the  common  purple 
shells,  and  species  of  the  genera  Nassa,  Emargi- 
nula,  Pectunculus,  Mya,  Lucina  and  Cardium.  At 
Norwich  the  Red  Crag  becomes  estuarine.  The 
Forest  Bed  of  the  Norfolk  coast  may  be  a  part  of 
its  land  surface.  A  patch  of  Crag  is  found  north 
of  Penzance,  at  St.  Erth,  98  feet  above  the 
sea.  A  more  interesting  deposit  on  the,  summit 
of  the  Chalk  descends  into  pipes  in  the  Chalk 
at  Lenham  in  Kent,  indicating  that  denudation 
has  removed  the  Crag  from  the  surface  of  the 
country. 

All  through  the  crag  the  temperature  on  the 
east  coast  was  becoming  colder.  This  is  evinced 
by  the  presence  of  stones  in  the  newer  crag  which 
appear  to  have  been  floated  southward  in  ice; 
and  it  may  be  indicated  by  the  increasing  number 
of  shells  which  at  the  present  day  characterise 


1 82  THE  STORY  OF  THE  EARTH. 

northern  and  arctic  seas.  Eventually  the  crag 
land  was  covered  with  boulder  clay,  and  the 
whole  country  experienced  glacial  conditions. 
The  cold  is  attributed  by  some  to  change  of 
form  in  the  earth's  orbit,  by  which  the  winters 
increased  in  length.  Others  attribute  it  to  up- 
heaval of  land.  Upheaval  of  Scandinavia  and 
the  North  Sea  would  displace  the  shells  south- 
ward, and  lead  to  a  condensation  of  vapour,  from 
which  glaciers  would  result  large  enough  to  cross 
the  plain  of  the  North  Sea  and  reach  Britain. 


CHAPTER  XXIII. 

GLACIAL    PERIOD    AND    GRAVELS. 

So  manifest  a  break  in  the  succession  occurs 
with  the  superposition  of  the  Glacial  deposits 
upon  the  Crag,  that  some  geologists  regard 
them  as  beginning  a  fourth  great  division  of 
the  strata  which  is  named  Quaternary  or  Post- 
tertiary.  Others  place  them  in  a  division  of  the 
Tertiary  period,  which  is  named  Pleistocene. 
The  singular  feature  of  the  formation  which 
justifies  a  separate  name  is  the  wide  spread  of 
the  glacial  conditions  over  the  Earth.  In  many 
countries  where  ice  now  is  only  a  passing  inci- 
dent of  Winter,  clays  are  found,  blue,  purple,  or 
brown,  full  of  fragments  of  rocks  which  are 
mostly  local,  though  many  have  travelled  from 
distant  places.  These  boulders,  which  cause  the 
deposit  to  be  named  Boulder  Clay,  are  often 
smoothed  and  grooved  or  scratched  on  one  side 


GLACIAL   PERIOD  AND  GRAVELS.  183 

like  stones  which  have  travelled  in  the  sides  or 
bed  of  a  Glacier.  The  deposit  is  often  indis- 
tinguishable from  the  clay  found  in  Alpine  val- 
leys, from  which  Glaciers  have  retired  which  once 
covered  the  country.  The  high  ground  in  every 
land  in  which  Boulder  Clay  is  found  supports  this 
inference  with  evidences  of  the  work  of  ice. 
The  Mountains  of  Scotland,  the  Lake  district 
of  England,  and  the  Snowdon  district  in  Wales 
are  smoothed  and  grooved  by  sheets  of  ice  which 
have  passed  away.  Small  joints  in  the  old  slates 
have  been  widened  and  deepened  in  the  valleys, 
until  rounded  structures  have  been  produced  like 
the  backs  of  huddled  sheep  at  rest.  This  condi- 
tion known  as  Roches  moutonndes  is  sometimes 
exposed  by  a  retreating  glacier  in  the  Alps,  and 
is  manifestly  due  to  the  work  of  frost  and 
glacier  ice. 

Above  many  a  mountain  valley,  such  as  the 
Pass  of  Llanberis,  angular  stones  are  perched  in 
positions  where  water  could  never  have  left 
them.  They  are  regarded  as  having  been  the 
stones  of  moraines  once  carried  on  the  surface 
of  a  glacier,  and  left  behind  in  their  present 
places  when  the  ice  melted  beneath  them.  The 
great  blocks  of  crystalline  rock  above  Netichatel 
are  of  the  same  substance  as  the  Mont  Blanc 
chain,  and  could  only  have  reached  their  present 
position  upon  the  limestone  chain  of  the  Jura  by 
crossing  the  central  valley  of  Switzerland.  On 
such  evidence  Glacial  conditions  for  a  country 
may  be  inferred  even  though  boulder  clay  is  not 
seen. 

In  North  America  Sir  J.  W.  Dawson  has 
described  the  evidences  of  the  Canadian  ice-age 
as  comprising,  (i.)  a  Lower  Boulder  Clay,  which 


184        THE  STORY  OF  THE  EARTH. 

rests  upon  a  glaciated  and  grooved  surface  of 
rock ;  (ii.)  The  Lower  and  Upper  Leda-clay  with 
marine  shells  and  drift  plants  ;  and  (iii.)  an 
Upper  Boulder  Clay  with  the  shell  Saxicava,  and 
gravel.  The  Lower  Boulder  Clay  forms  the 
basins  of  the  great  Canadian  lakes.  The  boul- 
ders are  mostly  of  Laurentian  gneiss.  Their 
striation  is  attributed  to  the  grating  of  pebbles 
included  in  shore-ice  upon  the  rocky  floor  be- 
neath, when  moved  by  the  tide. 

In  Britain  the  glacial  deposits  are  spread 
irregularly.  They  consist  of  Upper  and  Lower 
Boulder  Clays  on  the  east  coast,  divided  by 
Middle  Glacial  Sands  with  marine  shells. 

The  granite  of  Criffel  in  Kirkcudbrightshire 
is  found  in  the  boulder  clay  over  Lancashire  and 
North  Wales.  Boulders  of  Volcanic  rocks  from 
Cumberland  are  scattered  over  Cheshire.  Dis- 
tinct streams  of  glacial  drift  extended  down  both 
the  east  and  west  sides  of  Britain.  The  boulders 
of  Westmoreland  Shap  granite  found  over  the 
plain  of  York  and  between  Whitby  and  Scar- 
borough on  the  coast,  prove  that  boulders  were 
also  distributed  eastward  from  local  centres,  not- 
withstanding the  Scandinavian  source  of  many 
rocks  in  the  Boulder  Clay  on  the  Norfolk  Coast 
at  Cromer.  The  Boulder  Clay  found  near  Lon- 
don at  Finchley,  and  at  Hornchurch  in  Essex,  is 
full  of  travelled  ice-grooved  rocks,  with  fossils 
from  the  secondary  strata  of  Yorkshire  and  Lin- 
colnshire. Glacier  ice  transported  the  rock  mat- 
ter, but  probably  shore-ice  and  icebergs  were 
partly  concerned  in  depositing  it,  so  as  to  fill  up 
the  old  valleys  and  leave  the  clay  on  the  surface 
of  the  country.  The  denudation  since  the  glacial 
period  has  been  very  great,  and  the  glacial  beds 


GLACIAL   PERIOD  AND   GRAVELS.  185 

are  cut  through  by  modern  valleys  which  are  ex- 
cavated in  the  underlying  deposits. 

In  many  parts  of  the  east  of  England  a  series 
of  gravel  beds  occurs  beneath  the  Boulder  Clay, 
and  in  these  pre-glacial  gravels,  chipped  flint  im- 
plements of  the  Palaeolithic  type  are  said  to  be 
found. 

In  the  east  of  England  the  Boulder  Clay  which 
caps  hills  is  itself  capped  by  coarse  hill  gravel 
which  has  the  aspect  of  being  boulder  clay  from 
which  the  clay  has  been  washed  out.  The  gravels 
descend  to  lower  and  lower  levels  till  they  occupy 
the  broad  shallow  troughs  through  which  exist- 
ing rivers  flow,  from  which  we  may  infer  that  ele- 
vation of  the  land  has  gradually  contracted  the 
width  of  existing  rivers.  Chipped  flint  imple- 
ments are  found  in  both  the  high  and  low  level 
gravels,  with  remains  of  mammals,  which  are 
mostly  African  in  their  affinities,  and  mostly  ex- 
tinct. They  include  species  of  Hippopotamus, 
Rhinoceros,  Elephas,  Lion,  Bear.  Deer,  Horse,  and 
Ox  survive  in  Britain. 

Evidences  of  severer  frosts  are  found  in  the 
broken  rock  fragments,  and  of  periodic  floods 
due  to  melting  of  the  snows.  The  leaves  of  the 
dwarf  birch  and  dwarf  willow  are  preserved  in 
clay  seams,  with  the  land  and  river  shells  which 
now  exist. 

As  hunter  or  as  husbandman  the  rude  fore- 
fathers of  the  British  people  left  in  rock  shelters 
and  caves  simple  works  of  art  which  show  that 
people  had  gained  a  primitive  civilization  who 
lived  when  the  post-glacial  gravels  were  formed, 
and  the  influence  of  glacial  conditions  was  still 
felt. 

The  dominance  of  man  over  animal  and  plant 


1 86  THE   STORY  OF  THE   EARTH. 

may  mark  the  beginning  of  a  new  geological  pe- 
riod; but  there  is  no  gap  in  time  or  change  in  life 
to  announce  the  human  period,  or  to  distinguish 
it  in  kind  from  earlier  epochs  in  the  story  of  the 
Earth, 


INDEX. 


Age  of  earth,  9. 

Alethopteris,  112. 

Alps,  18. 

Ammonites,  62,  95,  123,  127,  128. 

Andesites,  27,  28. 

Annularia,  112. 

Anodonta,  50,  97. 

Anomodontia,  117. 

Anorthite  in  meteorites,  12. 

Anthracite,  107. 

Araucarites,  109. 

Archaopteryx,  138. 

Archean  rocks,  78. 

Ash,  volcanic,  26,  30,  85. 

Asmanite,  12. 

Asterophylites,  112. 

Astronomy,  relation  to  geology, 

10.     • 
Augite  in  meteorites,  12. 

B. 

Basalt,    IT,    27;    varieties    of,    29; 

columnar  structure  in,  30. 
Bclemnites,  60,  127,  128,  142. 
Birds,   fossil,   138.   154. 
Bituminous  coal,  107. 
Blastoidea,  69. 
Boulders,  34. 

Brachiopoda,  69,  83,  85,  101. 
Branchiosaurus,  117. 
Bronzite  in  meteorites,  12. 


C. 

Catamites,  112. 
Calcareous  sandstone,  40. 
Cambrian  period,  67,  81. 
Carboniferous  period,  97. 


Cave  earth,  43. 

Cephalopoda,  94. 

Cerastes,  123. 

Chalk,   formation  of,  48. 

Chalk  period,  the,  156. 

Clay,  42,  53>  54;  colouring  mat- 
ter of,  43;  inflammable,  44; 
Scrobicularia,  33. 

Cleavage,  slaty,  20. 

Clymcnia,  94. 

Coal,  33,  98,  104. 

Conformity   of  strata,  56,  75« 

Conglomerates,  36. 

Coralline  Crag,  178. 

Coral  reefs,  47. 

Corals,  85,  87. 

Cordaitcs,  109. 

Crag,  the,  178. 

Cretaceous  rocks,  149. 

Crinoidal  limestone,  47,  48. 

Curculoides,  114. 

Current-bedding  in  clay,  43;  in 
sandstone,  39. 

Cyclas,  50. 

Cystoidea,  69.  0 

D. 

Dadoxylon,  109. 
Deserts,  31. 
Devonian  period,  92. 
Diabase,  29. 
Dinotherium,  177. 
Diorite,  27,  29. 
Dodo,  the,  68. 
Dolerite,  29. 
Dust,  volcanic,  26,  30,  85. 


Earthquakes,  14. 
Enaliornis,  155. 

187 


iSS 


THE   STORY    OF    THE    EARTH. 


Encrinites*  87,  100. 
Enstatite  in  meteorites,  12. 
Eocene,  or  Lower  Tertiary  pe- 
riod, 162,  178. 

Eophrynus  Prestwichi,  113. 
Eoscorptus,  114. 
Eozoon  canadense*  79. 
Etna,  lavas  of,  27,  29. 
Euphoberia.)  113. 
Eurypterus^  88,  89. 

F. 

Felspar  In  sandstone,  38. 
Fishes,    fossil,    88,    94,    96,    102, 

117,  i25}  179. 

Folding  in  rocks,  15,  18,  22. 
Foraminifera  of  chalk,  159. 
Fossils,  v,  20,  59,  62. 
Fuller's  Earth,  233. 

G. 

Gabbro,  25,  28. 
Gasteropoda^  102. 
Giant's  Causeway,  30. 
Glacial  period,  182. 
Gneiss,  22,  23. 
Goniatites,  95,  106,  123. 
Granite,  formation,  14,  27 ;  meta- 
morphism,  23  ;  composition,  24. 
Graphite,  78. 
Graptolites,  69,  85. 
Greensand,  Lower,  41,  151. 
Greensand,  Upper,  41,  152. 
Grisons,  18. 
Grits,  34,  37»  53- 
GrypJuea*  126. 

H. 

Heat  of  the  earth,  12. 

Hemiaspis,  88. 

Herschel,  Sir  John,  on    fluidity 

of  the  earth,  13. 
Hipparion,  73. 
Holloway,  Rev.  John,  60. 
Horse,  fossil  development  of,  73. 
Hunstanton  Limestone,  60. 
Huronian  rocks,  79. 
Hypsiprymus,  123. 

I. 

Ichthyosaurus,  125,  128. 

Inguanodon,  146,  147. 

Insects,  fossil,   114,   124,  133,  145. 


Iron,  in  meteorites,  n  ;  in  sand- 
stone, 38,  40. 
Iron  pyrites  in  clay,  44. 

J. 

Jura  mountains,  18. 
K. 

Kelvin,     Lord,     on    geological 

time,  13. 

Kimeridge  clay,  44. 
Krakatoa,  eruption  of,  26. 


Labradorite  in  meteorites,  12. 
LabyrintJwdontSi  114,  117,  120. 
Laurentian  period,  78. 
Lava,  formation  of,  14. 
Lepiaodendron,  104,  no. 
Leucite  in  basalt,  29. 
Lias  period,  125. 
Life,    distribution     of,    on    the 

earth,  63. 
Lignite,  33,  49. 
Limestone,  45,   52,   53  ;   Archean, 

78  ;  fresh-water,  49  ;  occurrence 

with  schists,  21,  23. 
Limnaa,  50. 
Lingula^  83. 
Lister,  Dr.?  59. 
Lithomantis*  114. 

1C. 

Mammals,    earliest    fossil,    123, 

Man,  glacial,  185. 

Maps,  geological,  59. 

Meandrina,  47. 

Megalosauria,  122,  134,  147. 

Melaphyre,  29. 

Merostomata,  69. 

Metals  in  volcanic  rocks,  27. 

Metamorphism,  23. 

Meteorites,  n. 

Mica  in  sandstone,  38. 

Microlestes,  123. 

Millepedes,  fossil,   113. 

"Millet  seed  beds,"  32. 

Millstone  grit,  37,  95,  102. 

Miocene  period,  173,  178. 

Mitchell,  Rev.  John,  60. 

Moa,  the,  68. 

Mountain  forming  rocks,  18, 


INDEX 


189 


Mountain  limestone,  100. 
Mud,  42. 
Myriapoda,  113. 


MynapO( 
Mytilus, 


86. 


N. 


Nautilus,  69. 
Neocomian  rocks,  142. 
Neoplagiaulax,  123,  166. 
Neritina,  50. 
Neuropteris,  112. 
Niagara  river,  v,  10. 
Nickel  in  meteorites,  II. 
Nummulitcs,  62. 

O. 

Obsidian,  28. 
Odontopteris,  112. 
Old  red  sandstone,  92. 
Oligocene  period,  178. 
Oliyine  in  meteorites,  12. 
Oolite  period,  45,  130. 
Ordovician  period,  81. 
Origin  of  earth,  9. 

P. 

Palaosaurus,  122. 

Palccotherium,  176. 

Paludina,  50. 

Pareiasauria,  118,  120. 

Peat,  32. 

Pebble  beds,  34,  53. 

Pennystone,  106. 

Peridolite,  30. 

Permian  period,  115. 

Phonolite,  29. 

Pipe  clay,  42. 

Plagiaulax,  123,  166. 

Planorbis,  50. 

Plants,    fossil,    69,    96,    108,    129, 

144,  149,  167,  169,  177. 
Pleswsauna,  125,  128. 
Pleurosternon,  145. 
Pliocene  period,  178. 
Plutonic  rocks,  25,  26. 
Polyzoa,  of  Coralline  Crag,  179. 
Porites,  47. 
Protocystites,  83. 
Protospongia,  83. 
Pterodactyl,  146. 
Pteropoda,  83,  84. 
Pterygotus,  88,  96. 
Puddingstone,  36. 
Pumice,  28. 


Q. 


Quartz  in  meteorites,  12. 

R. 

Rain-prints,  54. 
Ramsey,  Sir  Andrew,  75. 
Reptiles,  fossil,   117,   125. 
Rhyolite,  27,  28. 
Ripple  marks,  41,   54. 
Roches  montonnees,    183. 
Rocky  Mountains,   18. 
Rugosa,   69. 
Rynchosauria,  122. 

S. 

Sand,   37,   53- 

Sand  dunes,   31. 

Sand  grains,   rounding  of,   31. 

Sandstones,  54;  colouring  of,  38. 

40;  occurrence  with  schists,  22. 
Scelidosaurus,    126. 
Schists,  21. 

Scorpions,  fossil,  114. 
Sea-eggs,  89. 
Selenite,  44. 
Septaria,  44. 
Sequoia,  18. 
Serpentine,  30. 

Shrinkage  of  earth's  crust,   15. 
Sigillaria,    104,    no. 
Siliceous  sandstone,   40. 
Silurian  period,  86. 
Slate,   19- 
Smeaton,  60,  61. 
Smith,  William,   59,  61. 
Sphenophyllum,    112. 
SphenopteriSf   112. 
Spherulites,  28. 
Spiders,  fossil,   113. 
Spongilla,  50. 
Stigmaria,    in. 
Strachey,  John,   60. 
Strata,   53;  classification  of,  74. 
Stratification,      contemporaneous, 

51;  laws  of,  58. 
Sun-cracks,   54. 
Superposition  of  strata,  58. 
Syenite,  25,  27. 

T. 

Temperature  of  the  earth,   12. 
Terrestrial   rocks,    31. 
Tertiary  period,  160. 


190 


THE   STORY   OF   THE   EARTH. 


Theriodontia,  118. 

Time,  geological,  v,  10,  13. 

Trachytes,  27. 

Triar  period,  120. 

Tridymite,  12,  28. 

Trilobitcs,  62,  69,  85,  90. 

Troxites,  114. 

U. 

Unconformity  of  strata,  57,  74. 
Uniot  50. 

V. 

Variation  in  species,  71. 
Vesuvius,  lavas  of,  27,  29. 
Volcanic  ash,  26,  30,  85. 


Volcanic  rocks,  26. 
Volcanoes,  14;  extinct,  16. 


W. 

Water,    agency    of,    in    volcanic 

action,  16,  26. 
Wenlock  limestone,  87. 
Whitehurst,  John,  61 
Wind  as  a  geological  agency,  31. 


Xylobius,  113. 
Zeuglodon,  174. 


X. 


Z. 


(10) 


THE    END. 


TA  02372 


SM- 
Rio 


